tim hieu ve giao thuc smtp

8/2/2019 Tim Hieu Ve Giao Thuc SMTP

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CHNG 3CAC NGHI THC TRUYEN NHAN

----b----Cong viec phat trien cac he thong Mail (Mail System) oi

hoi hnh thanh cac chuan ve Mail. ieu nay giup cho viecgi nhan cac thong iep c am bao , lam cho nhngngi cac ni khac nhau co the trao oi thong tin chonhau.

Co 2 chuan ve Mail quan trong nhat va c s dungnhieu nhat t trc en nay la X.400 va SMTP ( Simple MailTransfer Protocol). SMTP thng i kem vi chuan POP3 va dohan che cua SMTP ma ngay nay ngi ta dung chuan mrong cua no la ESMTP (Extended SMTP). Muc ch chnh cuaX.400 la cho phep cac mail co the c truyen nhanthong qua cac loai mang khac nhau bat chap cau hnh

phan cng, he ieu hanh mang , giao thc truyen danc dung. Con muc ch cua chuan SMTP mieu ta cachieu khien cac thong iep tren mang Internet. ieu quantrong cua chuan SMTP la gia nh may nhan phai dunggiao thc SMTP gi Mail cho 1 Server luon luon hoatong. Sau o, ngi nhan se en lay Mail cua ho tServer khi nao ho muon dung giao thc POP (Post OfficeProtocol), ngay nay POP c cai tien thanh POP3 (PostOfficce Protocol vertion 3). Cac giao thc Mail thong dung :chuan X.400, chuan MAIP, SMTP (ESMTP), POP3 . aych trnh bay chi tiet ve POP3 va SMTP .

Phan 1Giao thc SMTP(Simple Mail transfer

Protocol )-----***-----

Bo phan chnh cua he thong Internet Mail chnh la cacMTA ( Message Transfer Agent), cac MTA gi 1 vai tro quan trongtrong viec chuyen giao email. V du sau khi mot ngi s dunggi mot bc mail ti hang i message, MTA se lay o vachuyen no ti mot MTA khac. Qua trnh o se tiep tuc tiepdien cho en khi message en c ni nhan. e co the lienlac vi cac MTA thong qua ket noi TCP cac MTA cua hethong Internet Mail co the s dung nhieu nghi thc khac nhaue chuyen giao cac thong tin (X400,ESMTP,....), Nhng ay tach xet nghi thc SMTP. ay la mot nghi thc cho phepchuyen mail t iem nay sang iem khac cho en ch tren


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mang Internet. No c cau tao bi tap cac cau lenh eClient co the yeu cau Sever thc hien mot so tac vu vatap cac cau tra li e Server hoi ap lai cho Client ve ketqua thc hien cac tac vu o. Mot chng trnh muon gic mail th no phai biet a ch cua mot SMTP server. Server

nay co nhiem vu chuyen mail en ni can thiet.

I- Gii thieuMot ac trng quan trong cua SMTP la kha nang chia ca Mail

qua moi trng dch vu giao chuyen, mot dch vu giao chuyencung cap mot moi trng truyen thong lien qua trnh(Interprocess Communication Environment IPCE ). Mot moi trngtruyen thong lien qua trnh co the bao gom mot Network,vai Network, hay mot tap hp con cua Network. ieu o quan

trong cho viec thc hien he thong giao chuyen (hay cac IPCE)one-to-one vi Network, mot qua trnh co the giao tiep vimot qua trnh khac thong qua viec nhan biet IPCE. Mail lang dung hay la cach dung cua giao tiep lien qua trnh, Mailco the giao tiep gia cac qua trnh trong nhng IPCE khacbang cach chia ca thong qua mot qua trnh c ket noi enhai (hay nhieu ) IPCE. Chi tiet hn Mail co the chia ca gianhng Host tren he thong giao chuyen khac nhau bang motHost tren ca hai he thong chuyen giao.

II- Mo hnh SMTPSMTP c thiet ke da tren mo hnh giao tiep sau: nh

ket qua cua mot yeu cau Mail cua user . Sender- SMTP thietlap mot kenh hai ng van chuyen en mot receiver- SMTP .Receiver- SMTP co the la ch en cuoi cung hay mot trunggian. Nhng lenh SMTP c sinh ra bi Sender-SMTP gi enReceiver- SMTP. Nhng reply SMTP c gi t Receiver- SMTPen Sender- SMTP trong s ap ng cho nhng lenh o.

Khi mot kenh giao chuyen c thiet lap sender-SMTP gii 1 lenh Mail bieu th cho Sender cua mail o. Neu Receiver-SMTP co the chap nhan mail, no tra li vi mot OK reply.Sau o Sender-SMTP gi mot lenh RCPT nhan dien Receivermail neu Receiver-SMTP co the chap nhan mail no tra li vi1 OK reply neu khong no se li vi 1 reply bac bo receivero (nhng khong phai toan bo s giao dch o). Sender- SMTPva Receiver- SMTP co the ieu nh vi vai recipient, khi nhngrecipient a c dan xep Sender-SMTP gi mail data ket thucvi mot chuoi ac biet neu receiver x ly mail data thanh


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cong no tra li vi 1 OK reply. Cuoc hoi thoai mot cachchu y lock step (one-at-a-time).

S o tren la mo hnh cho cach dung SMTP.SMTP cung cap nhng c che giao chuyen Mail mot cach

trc tiep t Host cua User gi en host cua user nhan khi cahai host c ket noi en cung dch vu giao chuyen hay qua

nhieu SMTP-Sever tiep van khi host xuat phat hay ch enkhong c ket noi en cung dch vu chuyen giao. e cothe cung cap kha nang tiep van SMTP-Sever phai c cungcap ten cua host en cung chang han nh han cua Mailhosten .

oi so cua lenh mail la 1 reverse-path no ac ta mailo t au en; oi so cho RCPT la 1 Forward-path no acta mail o i en au. Forward-path la mot lo trnh nguon,reverse-path la mot lo trnh tr ve (no co the c dunge tra ve mot message cho sender- khi xay ra loi vi 1message c tiep van).

Khi cung mot message c gi cho nhieu recipient SMTPkhuyen khch chuyen giao ch mot ban sao cua data cho tatca cac Receiver cung mot host ch.

Nhng command va reply mail co nhng cu phap khackhe. Nhng reply cung co mot ma so. Trong nhng th du theosau se xuat hien nhng lenh (commands) va nhng tra li(replies) , mot danh sach cac lenh va reply hoan chnh trongphan 4.

Cac command va reply khong phan biet kieu ch hoa haythng. Lu y, ieu nay khong ung vi ten cua Usermailbox. Cho mot so host ten cua user co phan biet kieu

ch, SMTP phai thi hanh ay u viec nhan kieu ch va gign kieu ch cua nhng user name nh chung a xuat hientrong nhng oi so cua mailbox. Host names khong phan bietkieu ch.

Cac command va reply la nhng ky t c tao ra t tapky t ASCII{1}, khi dch vu van chuyen cung cap mot kenhchuyen giao 8 bit (octet). Moi mot ky t 7 bit c truyen ung

SenderSMTP

ReceiverSMTP

User

FileSyste

m

File

System

SMTP

Commands/Replies

and Mail

Sender-SMTPReceiver-

SMTP


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bang cach chuyen no ve he 8 (octet) vi bit co th t caonhat b xoa ve 0.

Khi ac ta cau truc thong thng cua command va reply,mot oi so (hay mot ky hieu ac biet ) se c bieu thbang mot bien meta-linguistic (hay mot hang so), v du nh :

, hay . ay dau ngoac nhon chnh chung la nhng bien meta-linguistic. Tuy nhien cac oiso th dung dau ngoac nhon mot cach literal. V du nh, motreverse-path thc c bao trong dau ngoac nhon nh, la mot trng hp cua (dau ngoac nhon c giao chuyen trongcommand va reply la ma thc cua no).

III . Mail1- Khai quat :

Co 3 bc cho s giao dch SMTP mail. Giao dch c bat

au vi yeu cau Mail mang s nhan dien sender, tiep theosau la mot chuoi cua mot hay nhieu lenh RCPTtrao nhngthong tin cua receiver, sau o mot lenh DATA cho mail data.Vacuoi cung la phan ch nh ket thuc mail data xac nhan giaodch o. Bc au tien trong thu tuc la lenh MAIL...

cha mailbox nguonMAIL FROM :

Lenh nay bao cho receiver biet mot giao dch mail mi sebat au va e reset tat ca cac bang trang thai va cacbuffer cua no bao gom tat ca recipient hay mail data. No phatra reverse-path co the c dung e bao loi. Neu c chapnhan receiver-SMTP tra ve mot reply 250 OK.

co the cha nhieu hn motmailbox. la mot lo trnh nguon tr ve liet kecac host va mailbox nguon. Host au tien trong reverse-path sela host gi lenh nay. Bc th hai trong thu tuc nay la lenh RCPT

RCPT To : Lenh nay phat i mot forward-path nhan dien recipient.

Neu c chap nhan receiver-SMTP tra ve mot reply 250 OK.Va lu lai forward-path. Neu recipient khong nhan biet threceiver tra ve reply 550 Failure. Bc th hai cua thu tucnay co the lap lai nhieu lan.

Forward-path co the cha nhieu hn mot mailbox.Forward-path la lo trnh nguon liet ke cac host va mailboxch. Host au tien trong se la host nhanlenh nay.


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Bc th ba trong thu tuc la lenh DATADATA

Neu chap nhan receiver-SMTP tra ve mot reply 354 va coitat ca cac dong noi tiep o la message text. Khi van bancuoi cung c nhan va lu tr receiver-SMTP gi mot

reply 250 OK.

Ke t mail data c gi tren kenh chuyen giao, iemket thuc cua mail data phai c ch nh e hoi thoaicommand va reply co the bat au tr lai. SMTP ch nh ketthuc cua mail data bang cach gi mot dong cha ch motdau cham.

Chu y rang mail data bao gom nhng muc (item) memoheader chang han nh Subject, To, Cc, From.

Phan ch nh ket thuc cua mail data cung xac nhan sgiao dch mail va bao cho receiver-SMTP biet e x ly viec lu

tr recipient va mail data ngay luc o. Neu c chap nhanreceiver-SMTP tra ve mot reply 250 OK. Lenh DATA se ch failneu giao dch mail khong hoan thanh (v du khong co receiver)hoac neu tai nguyen khong co hieu lc.

Thu tuc tren la mot v du cua mot giao dch mail. Nhnglenh nay ch c dung trong nhng trat t c trnh bay tren. V du :

Mot minh hoa cach dung nhng lenh nay tronut; end with .

S: Blah blah blah...S: ...etc. etc. etc.

S: .R: 250 OKBay gi mail c chap nhan cho Jones va Brown. Green

khong co mot mailbox tren Beta host.

2- S nh hng :Co mot so trng hp thong tin cua ch en trong

b sai nhng receiver-SMTP biet ch en ung.Trong trng hp nh vay mot trong nhng reply sau se cdung e cho phep sender tiep xuc ch en ung :

251 User not local; will forward to Reply nay ch cho receiver-SMTP biet mailbox cua user o

nam tren mot host khac va ch nh forward-path unge sau o s dung. Lu y mot trong hai host hay user hayca hai co the khac nhau . Receiver chu trach nhiem choviec phan phoi nhng message.


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551 User not local; please try Reply nay ch cho receiver-SMTP biet mailbox cua user

nam tren mot host khac va ch nh forward-path ung es dung . Lu y host hoac la user hay ca hai co the khacnhau . Receiver t choi chap nhan mail cho user A. Sender

phai nh hng lai cho mail o tuy theo nhng thong tinc cung cap hoac la tra tra li error cho user khiau.V du sau minh hoa cach dung cua nhng ap ngnay :

S: RCPT TO:[email protected]: 251 User not local; will forward to

HayS: RCPT TO:R: 551 User not local; please try [email protected]

3- Kiem tra va m rong :

SMTP cung cap them nhng iem ac trng, cac lenhe kiem tra mot user name hay m rong mot danh sach ach c lam vi lenh VRFY va EXPN no dung oi so kieuchuoi ky t. Vi lenh VRFY chuoi o la mot user name, vacau tra li(response) co the bao gom full name cua user ova phai bao gom mailbox cua user o. Vi lenh EXPN chuoio nh danh mot danh sach a ch va cau tra li conhieu dong co the cha full name cua cac user o va phaicha nhng mailbox tren danh sach a ch (mailing list).

Neu mot host c bo sung lenh VRFY hay EXPN th t nhatnhng mailbox cuc bo phai c tha nhan nh lausernames. Neu mot host chon la e tha nhan nhng chuoikhac nh user names th ieu o c cho phep.

Trong mot so host s phan biet gia mot mailing list vamot b danh cho single mailbox hi m ho. T o mot cau trucd lieu pho bien co the gi ca hai kieu phan t va noco the dung cac mailing list cua mot mailbox. Neu mot yeucau c tao ra e kiem tra mot mailing list mot cau tra likhang nh co the c cho neu tren message nhan c ac nh a ch no se c phan phat cho tat ca moingi trong danh sach o. Mat khac mot loi se c baocao (e.g., "550 That is a mailing list, not a user"). Neu mot yeucau c tao ra e m rong mot user name mot cau tra likhang nh co the c cau hnh bang cach tra ve motdanh sach cha mot ten hay mot loi co the c bao cao(e.g., "550 That is a user name, not a mailing list").

Trong trng hp mot reply nhieu dong (thng cho EXPN)la mot mailbox c ac ta tren tng dong cua reply omot cach chnh xac. Trong trng hp nay mot yeu cau
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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nhap nhang kho hieu nh : VRFY Smith co hai cau tra licua Smith phai la "553 User ambiguous". V du kiem tra mot user name

S: VRFY SmithR: 250 Fred Smith

Hay S: VRFY SmithR: 251 User not local; will forward to

HayS: VRFY JonesR: 550 String does not match anything.

HayS: VRFY JonesR: 551 User not local; please try

Hay

S: VRFY GourzenkyinplatzR: 553 User ambiguous.Trng hp m rong mot mailbox list oi hoi mot reply

nhieu dong xem trong v du sau: m rong mot mailing list (danhsach a ch)

S: EXPN Example-PeopleR: 250-Jon Postel R: 250-Fred Fonebone R: 250-Sam Q. Smith R: 250-Quincy Smith

R: 250- R: 250 Hay

S: EXPN Executive-Washroom-ListR: 550 Access Denied to You.

Nhng oi so chuoi ky t cua lenh VRFY va EXPNkhong the vt qua gii han c quyen tren s bo sung adang cua user name va khai niem mailbox. Tren mot so hethong no co the danh rieng cho oi so cua lenh EXPN ela mot file name cho mot file cha mot mailing list nhng lai comot qui c a dang cua viec ac ten file trong internet.

Lenh VRFY va EXPN khong c bao gom trong s thc thitoi thieu (trnh bay trong phan sau) va khong c oi hoie lam viec thay ca khi chung c thc thi.

4- Sending and Mailing :Muc ch chnh cua SMTP la phan phoi nhng message

en nhng mailbox cua user . Mot dch vu rat pho bien ccung cap bi mot so host la e phan phoi nhng message


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en nhng terminal cua user( cung cap cho user lam viec trenhost o) . S phan phat en nhng mail box cua user c goila mailing, s phan phat en nhng user terminal c goila sending. Bi v mot so host co s thc thi cua sendinggan giong vi s thc thi cua mailing chung la hai chc nang

c lien ket vi SMTP. Mac du lenh sending khong bao gomtrong yeu cau thc thi toi thieu( xem phan sau). Nhng userco kha nang ieu khien viec ghi message len nhng terminalcua ho. Hau het cac host cho phep chap nhan hay t choinhng message.

Ba lenh sau c nh ngha e cung cap nhng optioncho sending. Chung c dung trong giao dch mail thay cho lenhMAIL va cung cap cho receiver-SMTP nhng ng ngha giao dchac biet

SEND FROM:

Lenh SEND oi hoi mail data c gi en user terminal.Neu user o khong hoat ong (hay khong chap nhan nhngterminal message) tren host o mot reply 450 co the c tracho mot lenh RCPT. Giao chuyen mail thanh cong khi messageo c phan phat en terminal.

SOML FROM:

Lenh nay la SEND Or MAIL oi hoi mail data c phanphat en terminal cua user neu user o ang hoat ong (vachap nhan nhng message terminal) tren host o. Neu userkhong hoat ong (haykhong chap nhan terminal message) thmail data c a vao trong mailbox cua user . Giao chuyen mailthanh cong khi message o c phan phat en terminal haymailbox.

SAML FROM:

Lenh nay la SEND And MAIL oi hoi mail data c phanphat en terminal cua user neu user o ang hoat ong (vachap nhan nhng message terminal) tren host o. Trong nhngtat ca trng hp mail data c a vao trong mailbox cuauser. Giao dch mail thanh cong khi message o c phanphat en mailbox.

Nhng ma reply tng t c dung cho lenh MAIL cung

c dung cho nhng lenh nay.

5- Opening and Closing : Ngaythi iem ma kenh giao chuyen c open comot s trao oi e am bao nhng host o ang giao tiepvi nhng host khac.

Hai lenh sau c dung trong viec ong m kenhtruyen


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HELLO QUIT

Trong lenh HELLO host nay gi i nhng nhan danglenh cua no co the c dch nh "HELLO, I am ".

* V du m ket noi :

Opening R : 220 BBN-UNIX.ARPA Simple Mail Transfer ServiceReadyS : HELO USC-ISIF.ARPAR: 250 BBN-UNIX.ARPA

* V du ong ket noi :Closing S: QUITR :221 BBN-UNIX.ARPA Service transmission channel.

6- Chia ca (Relaying) :Forward-path co the la mot lo trnh nguon cua form

"@ONE, @TWO:JOE@THREE"

vi ONE ,TWO, THREE la cac host.Form nay c dung e nhan manh s phan biet giamot address va mot route. Mailbox la mot address tuyet oi,va route la thong tin ve viec lay chung nh the nao .

Nhng thanh phan cua forward-path c chuyen enreverse-path khi message o c chia ca t mot server SMTPen mot server-SMTP khac. Reverse-path la mot lo trnh nguontr ve (khac vi mot lo nguon la t v tr hien hanh cuamessage en iem khi au cua message o). Khi mot serverSMTP xoa phan nhan dang cua no trong forward-path vachen phan nhan dang cua no vao trong reverse-path, no

phai dung cai ten ma no c biet ti trong moi trngma no se gi vao, khong phai la moi trng ma mail to en, trong trng hp server-SMTP c biet en vinhng ten khac nhau trong nhng moi trng khac nhau.

Neu mot message en mot SMTP thanh phan au tiencua forward-path khong phai la phan nhan dang cua SMTPo, thanh phan nay khong b xoa trong forward-path va cdung e xac nh SMTP ke e gi message en. Trongtrng hp nay SMTP them phan nhan dang cua no vaoreverse-path..

Dung lo trnh nguon receiver-SMTP nhan mail e chia ca

en mot server-SMTP khac. Receiver-SMTP o co the chapnhan hoac bac bo cong viec chia ca cho mail, nh cach nochap nhan hay bac bo mail cho mot user cuc bo. Receiver-SMTP thay oi nhng oi so lenh bang cach chuyen phannhan dang cua no t forward-path vao cho m au cuareverse-path. Sau o receiver-SMTP tr thanh sender-SMTP, thietlap mot kenh truyen en SMTP ke trong forward-path,va gimail o cho no.


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Host au tien trong reverse-path se la host gi cac lenhSMTP va host au tien trong forward-path se la host cac nhancac lenh SMTP .

Lu yrang forward-path va reverse-path xuat hien trongcac lenh va cac reply SMTP, nhng no khong can thiet xuat

hien trong message . No khong can thiet cho nhng ngdan va cu phap ac biet nay xuat hien trong nhng fieldcua message header nh "To:" , "From:", "CC:",.

Neu mot server-SMTP chap nhan cong viec chia ca mailva sau o thay forward-path khong ung hay mail o khongthe c phan phat c v bat c l do nao, th no phaixay dng mot message thong bao "undeliverable mail" (mailkhong the phan phat) va gi no en ni xuat phat cuamail khong the phan phat o(c ch nh trong reverse-path). Message thong bao nay phai la t server-SMTP tai hosto. D nhien nhng server-SMTP se khong gi nhng message

thong bao ve nhng s co xay ra cho message thong baoo. Mot cach ngan chan s lap lai trong viec thong bao loila ac ta mot null reverse-path trong lenh MAIL cua messagemot thong bao. Khi mot message thong bao nh vay cchia ca no c dung e loai bo reverse-path null. Mot lenhMAIL vi null reverse-path nh di ay:

MAIL FROM:< >Thong bao nay nam trong tra li cho mot message

c khi ong bi JOE tai HOSTW va gi thong qua HOSTXen HOSTY vi ch th chia ca no en HOSTZ, no la bcau tien trong viec tra ve message thong bao .

V du message thong bao mail khong the phan phatS: MAIL FROM:R: 250 okS: RCPT TO:R: 250 okS: DATA R: 354 send the mail data, end with .S: Date: 23 Oct 81 11:22:33 S: From: [email protected]: To: [email protected]: Subject: Mail System ProblemS:S: Sorry JOE, your message to [email protected] lost.

S: HOSTZ.ARPA said this:S: "550 No Such User"S: .

R: 250 ok

8-Thay oi vai tro :Lenh TURN co the dung e ao vai tro cua hai chng

trnh ang giao tiep tren kenh giao chuyen.


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Neu chng trnh A ang la sender-SMTP hien hanh va nogi lenh TURN va nhan mot reply OK(250) th chng trnh A trthanh receiver-SMTP.

Neu chng trnh B ang hien hanh receiver-SMTP hienhanh va no gi lenh TURN va nhan mot reply OK(250) th

chng trnh B tr thanh sender-SMTP.e t choi thay oi vai tro receiver gi reply 502Lu y la lenh nay khong bat buoc. Thng no khong

c dung trong tnh trang kenh giao chuyen la TCP. Tuy nhienkhi tr gia cho viec thiet lap kenh giao chuyen cao, lenh nayco the rat co ch. V du nh lenh nay co ch trong viec hotr la trao oi mail dung he thong public switched telephonelam mot kenh giao chuyen, ac biet neu mot so host ec cac host khac cho viec trao oi mail.

IV. ac ta SMTP

A. Nhng lenh SMTP (Commands SMTP)1. Ng ngha lenh :Nhng lenh SMTP nh ngha s truyen mail hay chc

nang cua he thong mail c yeu cau bi user. Nhng lenhSMTP la nhng chuoi ky t ket thuc bang . Banthan ma lenh la nhng ky t ch (alphabetic) ket thuc bi neu co nhng tham so theo sau va khac. Cuphap cua nhng mailbox phai tuan theo nhng thoa hieppha receiver. Nhng reply SMTP c ban en trong phan B.

Mot s giao dch mail bao gom vai oi tng d lieuc giao tiep khi nhng oi so cho cac lenh khac nhau.

Reverse-path la oi so cua lenh MAIL. Forward-path la oi socua lenh RCPT. Va mail data la oi so cua lenh DATA. Ba oiso va nhng oi tng d lieu c duy tr cho en khi xacnhan truyen xong bi s ch nh ket thuc cua mail data ththat s ket thuc giao dch. Mo hnh cho no la nhng bufferrieng biet c cung cap e gi kieu cua oi tng dlieu. Mot so lenh ac trng sinh ra thong tin c gan vaomot buffer ac trng, hay lam cho mot hay nhieu buffer b xoa.

HELLO (HELO) : Lenh nay dung nh danh sender-SMTP enreceiver-SMTP. Field oi so cha host name cua sender-SMTP.

Receiver-SMTP nh danh no en sender-SMTP trong tra libat tay cho viec ket noi, va trong cau tra li cho lenhnay.Lenh nay va mot reply OK e xac nhan ca haisender-SMTP va receiver-SMTP ang trong tnh trang khi ong,ieu o la: khong co mot giao dch mail nao ang tienhanh va tat ca cac bang trang thai va buffer a cxoa.


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MAIL : Lenh nay c dung khi tao mot giao dch mailtrong o mail data c phan phoi en mot hay nhieumailbox. Feild oi so cha mot reverse-path. Rever _se - pathbao gom mot danh sach cac host tuy y va mailbox cuauser. Khi danh sach cac host hoan tat no la mot lo trnh

nguon tr ve va ch nh mail o c chia ca thong quamoi host tren danh sach o (host au tien trong list la hostchia ca gan nhat). List nay c dung nh mot lo trnhnguon e tra ve sender nhng thong bao khong thephan phat. Tai moi host chia ca no them phan nh danhcua ban than vao cho bat au cua list o va phaidung ten cua no c biet trong IPCE ni no se chia camail en o, ung hn la ICPE co mail en t o (neuchung khac nhau). Trong mot so loai message thong baoloi (v du thong bao mail khong the phan phat) reverse-path co the la null.

RECIPIENT (RCPT) : Lenh nay dung nh danh mot recipient(ngi nhan) mail data rieng le, nhieu recipient c acta bang nhieu lenh nay. Forward-path bao gom mot danhsach cac host tuy y va mot mailbox ch c yeu cau.Khi danh sach host o hoan tat. No la mot lo trnh nguonva ch nh mail phai c chia ca en host ke tiep trenlist o. Neu receiver-SMTP khong thc thi chc nang chia cano co the dung c reply nay va se cho mot unknownlocal user (550). Khi mail c chia ca, host chia ca phai chuyenphan nh danh no t cho bat au forward-path va atvao cho bat au cua reverse-path. Khi mail trai ra ti chcuoi cung (forward-path ch cha mot mailbox ch) receiver-SMTP Insert no vao trong mailbox ch trong s ong y vithoa hiep host mail cua no.

V du mail c nhan tai host chia ca A vi nhng oiso:

FROM:TO:Se c chia ca en host B vi oi so

FROM:TO:.Lenh nay sinh ra oi so forward-path cua no c gan

vao forward-path buffer.

DATA(DATA) : Receiver x ly nhng dong theo sau lenh naykhi mail data t sender en. No lam cho mail data t lenhnay c ghi vao data buffer. Mail data nay co the cha


13/43

nhng ky t cua 128 ma ACII. Data mail c ket thucbang mot dong ch cha mot dau cham. o la motday ky t ". " (xem phan 4.D.2). Va o lach nh ket thuc cua mail data.

S ch nh ket thuc mot chuoi oi hoi receiver

phai x ly viec lu tr nhng thong tin giao dch mail ngaylap tc. Qua trnh x ly nay dung thong tin trong reverse-path buffer, forward-path buffer, mail data buffer, va khi hoantat lenh nay nhng buffer o se b xoac nhan, nhng message c chia ca se co nhieu donganh dau thi gian.

Khi mot receiver-SMTP tao ra final delivery cua motmessage no insert vao cho bat au cua mail data motdong return-path . Dong return-path o bao quan thong tintrong reverse-path t lenh mail. ay deliver final congha la message o ri khoi the gii SMTP. Thong thng

co ngha la no a c chuyen en user ch . nhng trongmot so trng hp no co the c x ly na va vac giao chuyen bi he thong mail khac.

Co the cho mailbox trong return path la khac biet vimailbox that s cua sender, v du nh neu nhng tra lierror c dung phan phat mot loi ac biet ieu khienmailbox.

Hai oan trc y noi mail data cuoi cung se bat auvi mot dong return path theo sau la mot hay nhieu donganh dau thi gian , sau nhng dong nay se la phanheader va body cua mail data [2].

S e cap ac biet can thiet cho s tra li(response) va s hanh ong tiep na c yeu cau khiqua trnh x ly theo sau s ch nh ket thuc mail data las thanh cong cuc bo. ieu nay co the phat sinh neusau khi chap nhan mot vai recipient va data mail receiver-SMTP thay mail data o co the c phan phat en motso recipient thanh cong nhng lai khong the en nhngngi khac (v du nh xay ra van e ve viec ch nh vtr cua mailbox). Trong tnh trang nh vay cau tra li cholenh DATA phai la mot reply OK. Nhng receiver-SMTP phaisoan va gi ve ni xuat x cua message o mot message

thong bao undelivered mail. Mot thong bao n liet ketat ca cac recipient khong nhan c message, hay nhngmessage thong bao rieng le phai c gi cho tngrecipient mot , tat ca nhng thong bao mail khong thephan phat c gi dung lenh MAIL (ngay ca neu ketqua o t qua trnh x ly mot lenh SEND, SOML, hay SAML).


14/43

V du cho ng dan tra ve va nhan anh dauthi gian nhan

Return-Path:

Received: from GHI.ARPA by JKL.ARPA ; 27 Oct 81 15:27:39 PST

Received: from DEF.ARPA by GHI.ARPA ; 27 Oct 81 15:15:13 PSTReceived: from ABC.ARPA by DEF.ARPA ; 27 Oct 81 15:01:59 PSTDate: 27 Oct 81 15:01:01 PSTFrom: [email protected]: Improved Mailing System InstalledTo: [email protected] This is to inform you that ...

SEND (SEND) : Lenh nay dung khi tao mot giao dch mailtrong o mail data c phan phat en mot hay nhieuterminal. Field oi so cha mot reverse-path. Lenh naythanh cong neu message c phan phat en mot

terminal.Reverse-path bao gom mot list cac host va mailboxsender tuy y khi list o hoan tat, no la mot lo trnhnguon tr ve va ch nh mail a c chia ca thong quacac host trong list o (host au tien trong list la host chia cagan nhat) danh sach nay c dung nh mot lo trnhnguon e tra ve cho sender nhng thong bao ve vieckhong phan phat c. Khi moi host chia ca them phannh danh vao trong v tr bat au cua list , no phai dungten ma no c biet en trong IPCE ni no se chia ca mailti o , ung hn la IPCE co mail ti t o.

Lenh nay xoa reverse-path buffer, forward-path buffer vamail data buffer va chen thong tin reverse-path t lenh nayvao trong reverse-path buffer.

?????????? END OR MAIL (SOML) : Lenh nay dung khi tao mot giao

dch mail trong o mail data c phan phat en mot haynhieu terminal hay mailbox. Cho tng recipient, data mail cphan phat en terminal cua recipient neu recipient o anghoat ong tren host o (va chap nhan nhng terminalmessage ), mat khac la en mailbox cua nhng recipiento. Field oi so cha mot reverse-path . Lenh nay thanh

cong khi message c phan phat en mot terminal haymailbox.

Reverse-path bao gom mot danh sach cac host tuy yva mailbox cua sender . Khi danh sach cac host o hoantat, no la mot lo trnh nguon tr ve va ch nh mailo a c chia ca thong qua cac host tren danh sach (hostau tien trong danh sach la host chia ca gan nhat). Danhsach nay c dung nh mot lo trnh nguon tra ve cho


15/43

sender nhng thong bao ve viec khong the phan phat.Khi moi host chia ca them phan nh danh no vao cho batau cua danh sach o, no phai dung ten c biet entrong IPCE ni no se chia ca mail en o ung hn la IPCEco mail en t o(neu chung khac nhau).

Lenh nay xoa reverse-path buffer, forward-path buffer vamail data buffer va chen thong tin reverse-path t lenh nayvao trong reverse-path buffer.

SEND AND MAIL (SAML) : Lenh nay dung khi tao mot giaodch mail trong o mail data c phan phat en mot haynhieu terminal va cac mailbox. Cho tng recipient data mailc phan phat en terminal cua recipient neu recipient oang hoat ong tren host o (va chap nhan nhng terminalmessage ) va cho tat ca recipient th en mailbox cua cacrecipient o. Field oi so cha mot reverse-path . lenh nay

thanh cong khi message c phan phat en mailbox.Reverse-path bao gom mot danh sach cac host tuyy va mailbox cua sender. Khi danh sach hoan tat no lamot lo trnh nguon tr ve va ch nh mail a c chiaca thong qua cac host trong danh sach o(host au tientrong danh sach la host chia ca gan nhat ) Danh sach nayc dung nh mot lo trnh nguon tra ve cho sender nhngthong bao ve viec khong the phan phat. Khi moi hostchia ca them phan nh danh no vao cho bat au cuadanh sach o no phai dung ten ma no c biet entrong IPCE ma no se chia ca mail en o ung hn la IPCE

ma mail en t o(neu chung khac nhau).Lenh nay xoa reverse-path buffer, forward-path bufferva mail data buffer va chen thong tin reverse-path t lenhnay vao trong reverse-path buffer.????????

RESET (RSET) : Lenh nay nh ro giao dch mail hien hanhb huy bo. Cac sender, recipient, mail data a lu se b huybo va tat ca cac bang trang thai, cac buffer b xoa.Receiver phai gi mot reply OK.

VERIFY(VRFY) : Lenh nay yeu cau receiver xac nhan oi

so nh danh mot user. Neu no la mot user name, full namecua user o (neu receiver biet) va mailbox ac ta ay uc tra ve.Lenh nay khong anh hng en reverse-pathbuffer, forward-path buffer va data mail buffer.

EXPAND (EXPN) : Lenh nay yeu cau receiver xac nhan motmailing list ( danh sach a ch) va tra ve mot thanh phan


16/43

trong danh sach o. Full name cua cac user (neu biet) vanhng mailbox c ac ta ay u c tra ve trong motreply nhieu dong.

Lenh nay khong anh hng en reverse-path buffer,forward-path buffer va data mail buffer.

HELP (HELP) : Lenh nay lam cho receiver thong tin giup cho sender lenh HELP. Lenh nay co the nhan mot oi so(co the la ten lenh) va tra ve thong tin chi tiet.


NOOP (NOOP) : Lenh nay khong anh hng cac tham sohay cac lenh c a vao trc no, no ac ta khongco mot hanh ong nao khac hn la receiver gi mot replyOK.


QUIT (QUIT) : Lenh nay nh ro receiver phai gi mot replyOK va sau o ong kenh giao dch . Receiver se khongong kenh giao dch cho en khi no nhan va tra li cholenh QUIT (ngay ca neu co mot loi xay ra). Sender sekhong ong kenh giao dch cho en khi no gi mot lenhQUIT va nhan reply o (ngay ca neu co mot loi tra licho lenh trc o). Neu ket noi b ong trc thi gianmong muon receiver se lam viec nh va nhan c mot

lenh RSET (bo tat ca cac giao dch ang treo ma cha lam,nhng khong undo nhng giao dch a hoan tat trc o)sender se hanh ong nh neu lenh hay giao dch o trongqua trnh x ly nhan c mot loi tam thi (4xx).

TURN (TURN) : Lenh nay nh ro receiver phai gi mot tronghai reply sau: (1) reply OK va sau o nhan vai tro cua motsender-SMTP, hay (2) gi mot reply t choi va gi lai vai tromot receiver-SMTP.

Neu program-A hien tai la mot sender-SMTP gi motlenh TURN va nhan mot reply OK (250) th program-A trthanh receiver-SMTP sau o program-A se trong trang thaikhi ong ch neu kenh giao chuyen a c m, sau ono ch nhan mot chao hoi dch vu a san sang 220.

e t choi thay oi vai tro receiver gi mot reply 502.Co s han che trong trat t khi dung nhng lenh nay.au tien trong mot cuoc trao oi phai la lenh HELLO,

lenh nay co the c dung sau o trong mot cuoc trao


17/43

oi khac. Neu oi so trong lenh HELLO khong c chapnhan mot reply failure 501 phai c tra ve va receiver-SMTP o phai trong trang cu.

Nhng lenh NOOP, HELP, EXPAND va VRFY co the c

dung nhieu lan trong mot cuoc giao dch.Cac lenh MAIL, SEND, SOML, va SAML bat au mot giaodch mail. Khi bat au mot giao dch mail bao gom mot lenhkhi tao giao dch , mot hay nhieu lenh RCPT, va mot lenhDATA o la mot trat t . mot giao dch mail co the cbo qua bi mot lenh RSET co the co hay khong co nhieugiao dch trong mot cuoc trao oi (session).

Neu oi so cua lenh khi ong giao dch khong thechap nhan mot reply failure 501 phai c tra ve vasercer-SMTP phai nam trong trang thai cu. Neu nhng lenhtrong cuoc giao dch khong ung trat t mot reply failure 503

c tra ve va receiver-SMTP o phai nam trong trang thaicu.Lenh cuoi cung trong cuoc trao oi phai la lenh QUIT

va lenh QUIT khong the c dung nhieu lan trong motcuoc trao oi.

2- Cu phap lenh :Nhng lenh nay bao gom mot ma lenh theo sau la

mot field oi so . Ma lenh la bon ky t ch . Nhng ky tthng va hoa c x ly nh nhau . Vay nhng t sau ayco the ai dien cho lenh MAIL:

MAIL Mail mail MaIl mAIl ay cung dung mot so ky hieu trnh bay cho nhnggia tr cua tham so , chang han nh TO hay to cho forward-path. Ma lenh va nhng field oi so c tach ra bi mothay nhieu khoang trang. Tuy nhien ben trong nhng oi soreverse-path va forward-path kieu ch rat quan trong. Trongmot so host user vu khac vi user Vu.

Field oi so gom co mot bien chieu dai chuoi ky t,ket thuc vi chuoi . Receiver khong nhan hanh ongcho en khi nhan c chuoi nay.

Dau ngoac vuong bieu th mot field oi so tuy y. Neu

khong nhan chon la nay mot defaul phu hp se c apdung.

Sau ay la nhng lenh SMTP:HELO

MAIL FROM: RCPT TO: DATA


18/43

RSET SEND FROM: SOML FROM: SAML FROM: VRFY

EXPN HELP [ ] NOOP QUIT TURN

Cu phap cua nhng field oi so tren( dung ky hieuBNF co the ap dung c ay) c cho ben di. Kyhieu ch nh mo field co the c lap mot hay nhieulan.

::= ::=

::= "" ::= | "," ::= "@" ::= | "." ::= | "#" | "[" "]" ::= "@" ::= | ::= ::= | ::= | ::= | | "-"

::= | "." ::= | ::= """ """ ::= "\" | "\" | | ::= | "\" ::= "." "." "." ::= | ::= ::= the carriage return character (ASCII code 13) ::= the line feed character (ASCII code 10) ::= the space character (ASCII code 32)

::= one, two, or three digits representing a decimalinteger value in the range 0 through 255 ::= any one of the 52 alphabetic characters A through Z

in upper case and a through z in lower case ::= any one of the 128 ASCII characters, but not any

or ::= any one of the ten digits 0 through 9 ::= any one of the 128 ASCII characters except ,


19/43

, quote ("), or backslash (\) ::= any one of the 128 ASCII characters (no exceptions) ::= "" | "(" | ")" | "[" | "]" | "\" | "."

| "," | ";" | ":" | "@" """ | the controlcharacters (ASCII codes 0 through 31 inclusive and 127)

Chu y dau suyet ngc \ la mot ky t nh at, noc dung ch nh ky t ke tiep c dung mot cachliteral (thay cho s thong dch thong thng cua no) v du nh"Van\,Sam" se c dung ch nh mot ky t mot field bayky t n vi dau phay la ky t th t cua field.

Thng nhng host c biet en bang nhng cai ten ,no c bien dch thanh a ch cua moi host. Lu y tenphan t cua domains phai la ten chnh thc, khong dungten hieu hay b danh.

Thnh thoang mot host khong biet en chc nang biendch va s giao tiep b khoa. e pht l chng ngai nay

hai cau truc dang so cung c chap nhan cho names cuahost. Mot dang la mot so nguyen he thap phan nam sauky hieu gii han # no ch nh so nay la a ch cuahost. Mot dang khac la bon so nguyen nho bao trong daungoac vuong va cach nhau bi nhng dau cham nh"[123.255.37.2]". No ch nh mot a ch 32 bit- ARPA internettrong bon field 8 bit.

Dong anh dau thi gian va dong ng dan tr vethng c nh ngha nh v du sau :

::= "Return-Path:"

::= "Received:" ::= ";" ::= "FROM" ::= "BY" ::= [] [] [] [] ::= "VIA" ::= "WITH" ::= "ID" ::= "FOR" ::= The standard names for links are registered with the

Network Information Center ( Ten chuan cho nhnglien ket c ang ky viNet Work Information Center) ::= The standard names for protocols are

registered with the Network Information Center.( Ten chuan chonhng protocol c ang ky vi Net Work InformationCenter)

::= ::=


20/43

::= ":" ":" ::= the one or two decimal integer day of the month in

the range 1 to 31. ::= "JAN" | "FEB" | "MAR" | "APR" | "MAY" | "JUN" |

"JUL" | "AUG" | "SEP" | "OCT" | "NOV" | "DEC"

::= the two decimal integer year of the century in therange 00 to 99.

::= the two decimal integer hour of the day in the range00 to 24.

::= the two decimal integer minute of the hour in therange 00 to 59.

::= the two decimal integer second of the minute in therange 00 to 59.

::= "UT" for Universal Time (the default) or other timezone designator

(as in [2]).

V du : Return PathReturn-Path:

V du : dong anh dau thi gian :Received: FROM ABC.ARPA BY XYZ.ARPA ; 22 OCT 81 09:23:59PDTReceive

h bay trong Sequencing cua phan V.3 va lc o trang thai

cua phan V.4Mot reply SMTP bao gom mot so ba ch so (ctruyen nh ba ky t ch so) theo sau la mot so van ban(text). So o c danh cho cac chng trnh t ong e xacnh trang thai a vao ke tiep. Text tren co y ngha chouser con ngi(khong phai may). Ba ch so o c an nhcha ay u thong tin c ma hoa sender-SMTP khong cankiem tra text o va co the huy bo hay chuyen no qua motuser thch hp. ac biet text nay co the oc lap vi receiverva oc lap vi ng canh, do co s giong nhau trong nhngtext khac nhau tng ma reply. Nguyen ly cua nhng ma

reply cho trong phu luc E. thong thng mot reply c nhngha la chuoi gom: mot ma ba ch so, , mot dongtext, va , hay mot reply nhieu dong (nh nh nghatrong phu luc E) ch nhng lenh EXPN va HELP co ket qua lanhng reply nhieu dong trong nhng tnh huong bnh thng,tuy nhien nhng reply nhieu dong c chap nhan cho nhieulenh.


21/43

1. Nhng ma Reply cho mot nhom cac chc nang:500 Loi cu phap, khong chap nhap lenh[no co the bao gom nhng loi nh: lenh quadai]501 Loi cu phap trong nhng oi so hay nhng

tham so lenh khong c cung cap dong lenh sai tham so cua lenh khong c cung cap

211 Trang thai he thong, hay tra li giup ve he thong

214 Thong iep giup [thong tin ve lam the nao e dung receiver

hay y ngha cua motlenh khong chuan ac biet ; reply nay rat co

ch cho ngi s dung]

220 dch vu san sang221 dch vu ong kenh giao chuyen421 dch vu khong dung c, ong

kenh giao chuyen[no co the la mot reply cho nhieu lenh neu

dch vu o biet replynay phai shut down]

250 Hanh dong mail yeu cau ok, hoan thanh251 User khong cuc bo, se hng en forward-

path450 Khong lay hanh ong mail yeu cau: mailbox

khong co hieu lc[chang han nh mailbox khong tm thay, khongtruy xuat c]

451 Bo qua hanh ong c yeu cau; loi trongqua trnh x ly

551 User khong cuc bo, vui long th lai

452 Khong nhan hanh ong c yeu cau : lutr cua he thong khong

u552 Bo qua hanh ong mail yeu cau: vt qua

ch nh lu tr553 Khong nhan hanh ong c yeu cau :

khong chap nhan tenmailbox [nh sai cu phap mailbox].

554 Khi ong viec nhan mail; ket thuc vi. giao

chuyen b sai.


22/43

2. Th t cua danh sach nhng ma Reply so :211 Tnh trang he thong, hay reply giup he

thong . 214 Thong iep giup .{thong tin lam the nao e dung receiver hay y

ngha cua mot lenh khong chuan ac biet ; replynay rat co ch cho ngi s dung]220 dch vu san sang221 dch vu ong kenh giao chuyen250 Hanh ong mail yeu cau OK, hoan thanh251 User khong cuc bo; se hng en

354 Khi ong viec nhap mail; ket thuc vi

.

421 dch vu khong s dung c,

ong kenh giao chuyen[no co the la mot reply cho nhieu lenh neu

dch vu o biet replynay phai shut down]

450 Khong lay hanh ong mail yeu cau;mailbox khong hieu lc

[nh mailbox ban]450 Bo qua hanh ong c yeu cau ; loi

cuc bo trong qua trnh x ly451 Khong nhan hanh ong c yeu cau;

lu tr cua he thong

khong u.500 Loi cu phap; khong chap nhan lenh

[no co the bao gom nhng loi nh: lenhqua dai]

501 Loi cu phap trong tham so hay oi so502 Lenh khong c cung cap503 Dong lenh sai504 Tham so cua dong lenh khong c

cung cap550 Khong nhan hanh ong c yeu cau ;

mailbox khong hieu lc

[nh mailbox khong tm thay hay khongtruy cap c]

551 User khong cuc bo; vui long th

552 Bo qua hanh ong ma mail yeu cau,vt qua ch nh lu tr

554 Khong nhan hanh ong c yeu cau; tenmailbox khong c


23/43

chap nhan. [nh sai cu phap mailbox] giaochuyen sai.

3. S lien tuc cua nhng Command & Reply :S giao tiep gia sender va receiver c nh la

mot cuoc hoi thoai tuan t do sender ieu khien. Chang hannh sender sinh ra mot lenh va receiver tra li vi mot reply.Sender phai ch s tra li nay trc khi gi them lenh.

Mot reply quan trong la chao hoi ket noi. Thongthng mot receiver se gi mot reply 220 service ready khiket noi hoan thanh. Sender phai ch thong iep chao hoinay trc khi gi cac lenh.

Lu y: tat ca cac reply kieu chao hoi dung ten chnhthc cua host server la t au

tien theo sau ma replyV du :

220 USC-ISIF.ARPA Service ready Bang ben di liet ke nhng reply thanh cong va thatbai cho moi lenh no phai c gia nhap vao mot cachnghiem ngat e; mot receiver co the thay the text trong cacreply nhng y ngha va hanh ong c nh bi ma so vabi chuoi command reply ac trng khong the b thay oi.

*-Nhng chuoi COMMAND-REPLYMoi lenh c liet ke vi cac reply co the cua no.

Nhng tien to c dung trc nhng reply co the la Pe khi au (khong dung trong SMTP) I cho phan gia, S

cho s thanh cong va E cho loi. Reply 421 (dch vu khonghieu lc, ong kenh giao chuyen) co the cho mot so lenhneu receiver-SMTP nhan biet rang no phai shut down. S lietke sau ay la cau truc c ban cho s o trang thai(statediagram) trong phan IV.C

CONNECTION ESTABLISHMENT (thiet lap ket noi)S: 220F: 421

HELLOS: 250E: 500, 501, 504, 421

MAILS: 250F: 552, 451, 452E: 500, 501, 421

RCPTS: 250, 251F: 550, 551, 552, 553, 450, 451, 452E: 500, 501, 503, 421


24/43

DATAI: 354 -> data -> S: 250F: 552, 554, 451, 452F: 451, 554E: 500, 501, 503, 421

RSETS: 250E: 500, 501, 504, 421

SENDS: 250F: 552, 451, 452E: 500, 501, 502, 421

SOMLS: 250F: 552, 451, 452E: 500, 501, 502, 421

SAMLS: 250F: 552, 451, 452E: 500, 501, 502, 421

VRFYS: 250, 251F: 550, 551, 553E: 500, 501, 502, 504, 421

EXPNS: 250F: 550

E: 500, 501, 502, 504, 421HELPS: 211, 214E: 500, 501, 502, 504, 421

NOOPS: 250E: 500, 421

QUITS: 221E: 500

TURN

S: 250F: 502E: 500, 503

C- S o trang thai (STATE DIAGRAM)Di ay la s o trang thai cho mot s thi hanh SMTP

n gian. Ch mot ch so au tien cua nhng ma replyc s dung . ay la mot bang trang thai cho tng nhom


25/43

lenh SMTP nhng nhom lenh nay c xac nh bang cachxay dng mot mo hnh cho moi lenh va sau o gom nhnglenh o lai vi nhau vi nhng mo hnh giong nhau ve cautruc.

Cho moi lenh co ba ket qua thanh cong (S), that

bai (F), loi (E) trong s o trang thai sau chung ta dung kyhieu B cho begin va ky hieu W cho wait for reply.

au tien s o trnh bay cho hau het cac lenh SMTP :

S o nay mo hnh cho nhng lenh sau:HELO, MAIL, RCPT, RSET, SEND, SOML, SAML, VRFY, EXPN, HELP,

NOOP, QUIT, TURN

Mot s o phc tap hn mo hnh cho lenh DATA :

Lu y: data ay la mot chuoi nhng dong gi t

sender en receiver khong can s tra li cho en khi dongcuoi cung c gi.

D- Chi tiet1. S thc thi toi thieu :

Lp le e lam cho SMTP co the lam viec, s thc thitoi thieu sau c yeu cau cho tat ca cac receiverCOMMANDS -- HELO

B

E

W S

F

2cmd

4,5

1,3

1,2B W

W F

S

EDATA

data

34,5

1,3

2

4,5


26/43

MAIL

RCPT

DATA

RSET

NOOP

QUIT

2. Tnh trong suot :Khong co mot s cung cap nao cho tnh trong suot d

lieu, chuoi ky t . ket thuc mail text va khongc user gi i. Thong thng user khong nhan biet c sngan can nhng chuoi ky t o. e cho phep tat ca cactext a soan thao cua user c truyen mot cach ro rangnhng thu tuc sau ay c s dung.

1>Trc khi gi mot dong mail text sender-SMTP kiem traky t au tien cua

dong o. Neu no la mot dau cham, mot dau cham phuc them vao au dong.2> Khi receiver-SMTP nhan mot dong mail text no kiem tra

dong o. Neu dong o ch co mot dau cham n th nola ket thuc cua mail. Neu ky t au tien la mot daucham va theo sau la nhng ky t khac nam tren cungdong. Th ky t au tien o b xoa.

Mail data co the cha cac ky t ma ASCII (128 ky t) tatca cac ky t c phan phat en mailbox cua recipient baogom phan nh dang va nhng ky t ieu khien khac. Neukenh chuyen giao cung cap mot luong d lieu 8 bit (octet),

nhng ma ASCII 7 bit tren c van chuyen ung ieu chnhlai trong he bat phan vi bit cao nhat b xoa ve 0.No co the can thiet e bien oi d lieu c nhan

hay lu tr . Trong mot so he thong, ieu nay can thiet chonhng host dung mot tap hp ky t khac vi tap ASCII , nhtap ky t cuc bo cua chung hay d lieu lu trong nhngrecord nhieu hn chuoi. Neu nhng thay oi tren la canthiet, chung phai khoi phuc lai( bien oi hai chieu) c neunhng bien oi o c ap dung cho mail c chia ca.

3. Kch thc :

Co vai oi tng oi hoi kch thc nho nhat lnnhat. o la tat ca tat ca s thc thi phai co e nhannhng oi tng co kch thc toi thieu, nhng khong batbuoc phai gi nhng oi tng ln hn kch thc nay

E CO PHAM VI LN NHAT CO THE,THC THI KY THUAT ANH LA

KHONG GII HAN CHIEU DAI CUA


27/43

user: Chieu dai tong cong ln nhat cua user name la 64

ky t. domain : Chieu dai tong cong ln nhat cua domain name

hay so la 64 ky t. path : Chieu dai tong cong ln nhat cua mot dong lenhbao gom nhng t lenh va la 512 ky t.

text line (dong van ban) : Chieu dai tong cong ln nhatcua dong van ban bao gom la 1000 ky t (khongtnh dau cham au c nhan len cho van e trongsuot).

recipients buffer: Tong so recipient ln nhat la 100recipient.

* Loi vt qua quyen c gii han co the c bao cao

bang cach dung nhng ma reply. V du nh :500 Line too long.(dong qua dai)501 Path too long (ng dan qua dai)552 Too many recipients.(qua nhieu recipient)552 Too much mail data (qua nhieu mail data)

V- Phu lucA. Dch vu van chuyen TCP

Transmission Control Protocol (ieu khien giao chuyen [3])c dung trong ARPA internet va trong mot so mang theo tieuchuan US DoD cho cac protocol internetwork .

* Thiet lap ket noi :Mot kenh giao chuyen SMTP la mot ket noi c thiet

lap the sender process port U and the receiver process port L. no lamot ket noi full duplex n gian c dung nh kenh ket noitren protocol nay c gan mot dch vu port 25 (31 he mi)o la L=25.

* Truyen d lieu :Ket noi TCP ho tr truyen nhng byte 8 bit. D lieu

SMTP la nhng ky t 7 bit ma ASCII. Moi ky t c truyennh mot byte 8 bit vi bit cao nhat b xoa ve 0.

B. Dch vu van chuyen NCPARPANET Host-to-Host Protocol [4] (c cung cap bi Network

Control Program) co the c dung trong ARPANET .* Thiet lap ket noi :Kenh giao chuyen SMTP c thiet lap qua NCP gia

sender process socket U va receiver process socket L. The InitialConnection Protocol [5] la ket qua la ket qua tiep theo motcap ket noi simplex. Cap ket noi nay c dung nh kenh


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giao chuyen . protocol nay c gan toan bo socket 25 , o laL=25.

* Truyen d lieu:Ket noi NCP data c thiet lap trong che o 8 bit . SMTP

data la nhng ky t ASCII 7 bit . Moi ky t c truyen nhmot byte 8 bit vi bit cao nhat b xoa ve 0.

C. NTTSNetwork Independent Transport Service [6] (dch vu van

chuyen mang oc lap) co the c dung .* Thiet lap ket noi :Kenh giao chuyen SMTP c thiet lap qua NTTS sender

process va receiver process . Sender process thi hanh CONNECT banau va ch receiver process thc thi ACCEPT ban au .

* Truyen d lieu :

Ket noi NTTS ho tr giao chuyen cac byte 8 bit . SMTP datala nhng ky t ASCII 7 bit . Moi ky t c truyen nh motbyte 8 bit vi bit cao nhat b xoa ve 0

D. Dch vu van chuyenX.25No co the dung X.25 service [7] cung cap bi Public Data

Networks mot cach trc tiep , tuy nhien no c e ngh motprotocol ang tin cay chang han nh TCP c dung trenket noi X.25.

E. Nguyen ly cua cac ma Reply

Ba ch so cua ma reply moi ch co mot y ngha acbiet. Ky t au tien bieu th response, good hay bad hay khonghoan tat. Mot sender-SMTP that se co the xac nhan hanhong ke tiep cua no (tien hanh theo ke hoach, lam lai, catgiam bt, ..) bang mot cach n gian la kiem tra ch soau tien nay. Mot ssender-SMTP muon biet mot cach ganung cac kieu loi xay ra (nh mail system error, commandsyntax error) co the kiem tra ch so th hai, e danh chso th ba cho viec ket thuc s sap at tang dan cuathong tin (the finest gradation of information. ) .

* Co nam gia tr cho ch so au tien cua ma reply: 1yz Positive Preliminary reply (reply khang nh ban au ) :

Lenh nay c chap nhan nhng hanh ong yeu cau sec gi hoan lai, tr hoan s xac nhan thong tin trong replynay. Sender-SMTP se gi mot lenh khac nh ro tiep tuc haybo qua hanh ong nay.[ Lu y: SMTP khong co lenh nao tha nhan kieu reply nay,vado o khong co lenh tiep tuc hay bo qua].


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2yz Positive Completion reply (reply khang nh s hoanthanh) :Hanh ong c yeu cau hoan tat mot cach thanh

cong, mot yeu cau mi co the c bat au . 3yz Positive Intermediate reply (reply khang nh gia chng) :

Lenh nay c chap nhan nhng hanh ong yeu cau sec gi hoan lai, tr hoan s nhan thong tin them. Sender-SMTP se gi mot lenh khac nh ro thong tin nay. Replynay c dung trong nhng nhom lenh tuan t.

4yz Transient Negative Completion reply (reply phu nh shoan thanh ngan han):Lenh nay khong c chap nhan va hanh ong yeu

cau khong xay ra, tuy nhien trang thai loi la tam thi, hanhong co the c yeu cau tr lai. Sender se quay tr laibat au chuoi lenh (neu co) kho gan mot ngha tc thicho no khi hai site khac nhau (receiverva sender- SMTPs) phai

ong y s thong dch. Moi reply loai nay co mot gia trthi gian khac nhau nhng sender-SMTP c khuyen khch thlai. Mot quy tac lat trang e xac nh neu mot reply acvao trong loai 4yz hay 5yz (xem ben di) th nhng reply o la4yz neu chung co the c lap lai ma khong can thay oig trong cau truc lenh hay trong nhng thuoc tnh cua senderhay receiver (nh mot lenh c lap lai mot cach giong nhauva receiver khong a ra mot s thc thi mi). 5yz Permanent Negative Completion reply (reply phu nh s

hoan thanh dai han):Lenh nay khong c chap nhan va hanh ong c

yeu cau khong xay ra . Sender-SMTP ngan can viec lap laiyeu cau (trong chuoi tuan t o). Ngay ca mot so hoancanh loi dai han co the hieu chnh c, do o ngi sdung muon hng sender-SMTP khi tao lai chuoi lenh obang cach ch ao hanh ong tai mot so thi iem trongtng lai(nh: sau khi chnh ta a c thay oi, hay user o thayoi trang thai account ) .

a/ Ch so th hai ma hoa nhng loai trali(response) ac trng :

* x0z Syntax: Nhng reply nay xem xet loi cu phap,nhng lenh ung cu phap khong a vao mot loai chcnang nao. Va khong thc thi cac lenh khong can thiet.

* x1z Information : Nhng reply nay e yeu cau thong tin,nh trang thai hay giup . * x2z Connections : Nhng reply nay tham khao en kenhgiao chuyen. * x3z : Cho en hien tai cha c ac ta.


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* x4z : Cho en hien tai cha c ac ta. * x5z Mail system : Reply nay ch nh tnh trang cua receivermail system vis-a-vis yeu cau truyen hay hoat ong he thongmail khac .

b/ Ch so th ba mang lai mot mc o y nghanhieu hn cho moi loai(category)c ac ta bi ch so th hai. Danh sach cac reply

minh hoa ieu nay. Moi reply text c e ngh nhieu hn lalenh, va co the thay oi tuy theo lenh vi nhng ket hpcua lenh o. Trong s kiem soat khac nhng ma reply nayphai theo s ac ta nghiem ngat trong phan nay s thc thicua receiver se khong phat sinh ra ma mi cho tnh trangkhac nhau khong ang ke cua nhng g c ac ta ay.Nhng nhng ma thch hp hn a c nh ngha san.

V du nh, mot lenh nh NOOP chang han no thc thi thanh

cong khong can e ngh sender-SMTP mot thong tin mi naose tra ve mot reply 250. Cau tra li la 502 khi lenh yeucau mot hanh ong non-site-specific khong thc thi c. Mots cai tien cho ieu o la reply 504 cho mot lenh c thcthi nhng no yeu cau mot tham so khong thc thi.

Reply text co the dai hn mot dong n, trong trng hpnay mot text hoan tat phai c anh dau do o senderbiet khi nao no co the ngng oc reply nay. ieu nay oihoi mot nh dang e ch nh mot reply nhieu dong.

nh dang cho cac reply nhieu dong quy nh tat ca cac

dong, chap nhan cho cuoi cung va bat au cua ma reply,theo sau o la mot dau gach noi - (dau tr) theo sau la textdong cuoi cung se bat au vi ma reply theo ngay sau ola , cac text va .

Cho v du:123-First line123-Second line123-234 text beginning with numbers123 The last line

Trong mot so trng hp sender-SMTP can tm ma replytheo sau la au dong, va pht l tat ca cac dong

trc. Mot t trng hp co d lieu quan trong cho sendertrong reply text sender se nhan biet trng hp nay t ngcanh hien hanh.

Phan 2


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Giao thc POP 3(Post Office Protocol version3)

-----***-----I . Gii thieu

Nghi thc POP3 c cai tien t nghi thc POP ( Post OfficeProtocol ).

Tren internet mot loai nao o nho hn node thng khongthc te e duy tr mot he thong van chuyen message(message transport system: MTS), v du nh mot workstation khongco u tai nguyen (recycle, disk space) hp le e cho phepmot SMTP server va mot he thong phan phat mail cuc boket hp gi thng tru va chay mot cach lien tuc . Thngth no co the rat at (hay khong thch hp) e gi motpersonal computer noi vi mot IP-style netwrork trong mot thigian dai (node o c biet se thieu tai nguyen nh

connectivity) .Mac du vay, e co the quan ly mail rat hu hieu tren

nhng node nho hn nay. Va chung thng ho tr mot useragent (UA) e giup cong viec ieu khien mail. e giaiquyet van e mot node co the cung cap mot thc the MTSa ra mot maildrop service en nhng node c cap nho hnnay. Post Office Protocol - Version 3 (POP3) c dung cho phepmot workstation truy xuat ong en mot maildrop tren motserver host. Thng ieu o co ngha la POP3 c dung echap nhan mot workstation goi mail c server ang gi chono.

Khi mot user agent tren mot client host mong muon a motmessage vao trong he thong van chuyen, no thiet lap motket noi SMTP en host chia ca cua no( host chia ca nay cothe, hay khong can POP3 server host cho client host o).

II. Thao tac c banBan au server host bat au mot POP3 service bang

cach lang nghe tren TCP port 110. Khi mot client host mongmuon dung POP3 service, no thiet lap mot ket noi TCP viserver host o. Khi ket noi c thiet lap, POP3 server gi motchao hoi. Client va server POP3 sau o trao oi nhng lenh vacac tra li cho en khi ket noi o c ong hay loai bo.

Lenh trong POP3 bao gom mot keyword (t khoa) theosau co the la mot hay nhieu oi so tat ca cac lenh cket thuc bi mot cap CRLF. Cac t khoa va oi so ctach rieng ra bi mot ky t trang n , t khoa dai 3 hay 4ky t. Moi oi so co the len en chieu dai 40 ky t.


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Cac tra li trong POP3 bao gom phan ch nh trangthai va mot t khoa co the theo sau la thong tin themvao. Tat ca cac tra li c ket thuc bi mot cap CRLF.Ch co hai loai tra li la: ch nh trang thai khang nh(+OK) va phu nh (-ERR) .

Tra li cho cac lenh la tra linhieu dong. Trongtrng hp nay, no cho phep ch nh mot cach ro rang,sau khi gi dong au tien cua cau tra li va mot CRLF,mot so dong them vao c gi i, moi dong ket thucbang mot cap CRLF. Khi tat ca cac dong cua tra li ac gi i bao gom mot so ket thuc he bat phan(termination octe) (ma 046 he mi, . ) va mot cap CRLF.Neu dong nao cua tra li nhieu dong bat au vitermination octet dong o la "byte-stuffed" bang cach (pre-pending) treotermina_ tion octe o cua dong tra li. Ke tay mot tra li nhieu dong c ket thuc vi nam octet

"CRLF.CRLF". Khi xem xet mot tra li nhieu dong client kiemtra xem neu dong o bat au vi termintion octet. Neu ungva neu nhng octet theo sau khac vi CRLF, octet au tiencua dong nay (termination octet) c bo i. Neu ung vaneu nhng ky t ket thuc theo ngay sau no, th tra li tPOP3 server nay c ket thuc vi mot dong cha .CRLFkhong c coi la mot phan cua tra li nhieu dong o.

Mot POP3 session tien hanh qua mot so trang thai trongthi gian song cua no. Khi ket noi TCP c m va motPOP3 server gi mot chao hoi. Hoi ngh se i vao trang thaiAUTHORIZATION (xac nhan). Trong trang thai nay client phai

nh danh no en POP3 server. Khi client nh danh thanh cong,server thu c nhng tai nguyen ket hp vi clients maildrop,va hoi ngh i vao trang thai TRANSACTION (giao dch). Trongtrang thai nay client yeu cau cac hanh ong trong vai trocua POP3 server khi client phat ra lenh QUIT, hoi ngh i vaotrang thai UPDATE. Trong trang thai nay giai phong cac tainguyen thu nhan c trong trang thai TRANSACTION va saygoodbye. Sau o ket noi TCP ong lai.

Mot POP3 server co the co mot timer t ong logoutkhong chu ong. Mot timer nh vayphai ton tai trongkhoang thi gian t nhat la 10 phut. Trong khoan thi gian

nhan cac lenh t client u e reset timer t ong logout o.Khi timer het hieu lc, hoi ngh khong i vao trang thaiUPDATE, server se ong ket noi TCP ma khong remove hay gimot message nao cho client.

III. Trang thai xac nhan (authorization state)Khi ket noi TCP c m ra bi mot cleint. POP3 server se

xuat ra mot dong chao hoi no co the la mot chuoi nao


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o c ket thuc bi CRLF.V du:

S: +OK POP3 server readyChao hoi o la mot POP3 reply. POP3 server bao gi

cung se truyen i mot tra li khang nh nh chao hoi

tren.POP3 session hien nam trong trang thai AUTHORIZATION.Client phai nh danh va xac nhan no vi POP3 server. Co haic che thch hp e thc hien. S ket hp lenh USER vaPASS , va lenh APOP.

e xac nhan dung s ket hp lenh USER va PASS. autien client phai phat mot lenh USER, neu POP3 server tra livi mot ch th trang thai khang nh (+OK), th client cothe phat i lenh PASS e hoan tat s xac nhan hay lenhQUIT e ket thuc POP3 session. Neu POP3 server tra li vimot ch th trang thai phu nhan (-ERR) cho lenh USER, th

client co the phat ra mot lenh xac nhan mi hay co thephat mot lenh QUIT.Khi client phat ra mot lenh PASS, POP3 server dung cap

oi so t lenh USER va PASS e xac nh neu client se ccho truy xuat en maildrop thch hp.

Khi POP3 server a c xac nh bang cac lenh xacnhan, no cho client truy xuat en nhng mailbox thch hp, sauo POP3 server thu c mot khoa truy xuat loai tr trenmaildrop, v s can thiet e ngan chan message b sa oihay b loai bo trc khi hoi ngh i vao trang thai UPDATE.Neu thu nhan khoa thanh cong POP3 server tra li vi mot

ch nh trang thai khang nh. Va luc nay hoi ngh i vaotrang thai TRANSACTION ma khong co message nao b anhdau e xoa. Neu maildrop khong m c v mot so l donao o(v du : mot khoa khong the nhan c, pha client bt choi truy cap ti maldrop thch hp o, hay maildrop khongc phan tch cu phap ), POP3 server tra li vi mot chnh trang thai phu nh (neu mot khoa c thu nhan nhngPOP3 server d nh tra li vi mot ch nh trang thai phunh, POP3 server phai giai phong khoa trc khi loai bo lenho ). Sau khi tra ve mot ch nh trang thai phu nh serverphai ong ket noi, neu server khong ong ket noi client co

the phat mot lenh xac nhan mi va bat au tr lai, hoacla client phat ra mot lenh QUIT.Sau khi POP3 server m c maildrop no gan mot

message-number cho moi message va bieu th kch thc cuamoi message trong he tam (octet), message au tien trongmaildrop c gan message-number 1, message th hai la 2 Trong cac lenh va cac tra li POP3 tat ca cac message-


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number va kch thc message c trnh bay da tren he 10(decimal)

. ay la nhng tom tat cho ba lenh POP3 ban luan tren :

USER name- oi so: Mot chuoi nh danh mot mailbox (c yeucau), no ch co y ngha vi server.- Gii han : Ch co the c cho trong trang thaiAUTHORIZATION sau khi POP3 chao hoi hay sau khi mot lenhUSER PASS khong thanh cong .- Cau tra li co the :

+OK ten mailbox co hieu lc-ERR khong chap nhan ten mailbox

V du:C: USER mrose

S: +OK mrose is a real hoopy frood...C: USER fratedS: -ERR sorry, no mailbox for frated here

PASS string- oi so: Mot password cho mailbox hay server (c yeu

cau)a server/mailbox-specific password (required)

- Gii han : Ch co the dc cho trong trang thaiAUTHORIZATION sau khi mot

lenh user thanh cong.- Discussion: (thao luan) : Ke t ay lenh PASS ch co

mot oi so, mot POP3server co the x ly khoang trong trong oi so nay nh

la mot phan cua password,thay v la e tach oi so ra .

- Cau tra li co the:+OK khoa maildrop va san sang-ERR password khong hieu lc-ERR khong c phep khoa maildrop

V du:

C: USER mroseS: +OK mrose is a real hoopy froodC: PASS secretS: +OK mrose's maildrop has 2 messages (320 octets)...C: USER mroseS: +OK mrose is a real hoopy froodC: PASS secret


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S: -ERR maildrop already locked

QUIT- oi so: khong-Gii han: khong

- Cau tra li co the:+OK

IV. Trang thai giao dch (transaction)Khi client nh danh no en POP3 server thanh cong va

POP3 server a khoa va m maildrop thch hp, POP3 sessionbay gi trong trang thai TRANSACTION client co the phatnhieu lan cac lenh POP3 sau ay. Sau moi lenh POP3 serverphat ra mot cau tra li. Cuoi cung client phat ra mot lenhQUIT va POP3 session i vao trang thai UPDATE .

ay la cac lenh POP3 co hieu lc trong trang thai

TRANSACTION: STAT

- oi so: khong- Gii han : Ch co the c cho trong trang thai

TRANSACTION.- Discussion: (thao luan) : POP3 server phat ra mot tra li

khang nh vi mot dong cha thong tin cua maildrop. Dongnay c goi la mot "drop listing" cho maildrop o.

Thch hp e phan tch cu phap mot cach n gian, tatca cac POP3 server yeu cau dung mot nh dang cho droplistings. Cau tra li khang nh gom co +OK theo sau la

mot khoang trang n, va kch thc cua maildrop trong hetam. Khong yeu cau cai g theo sau maildrop size.

Lu y: Viec ngan can mot cach manh me s thc thicac thong tin phu cung cap trong drop listing. Mat khacieu kien c ban luan sau, no cho phep client phantch cu phap cac message trong maildrop.

Chu y: Nhng message c anh dau xoa khong cem trong tong so

- Cau tra li co the:+OK nn mm

V du :C: STATS: +OK 2 320

LIST [msg]- oi so : Mot message-number (tuy y) co the khongtham khao en mot message c anh dau xoa.


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- Gii han : Ch co the c cho trong trang thaitransaction.

- Discussion: Neu mot oi so c cho va POP3 serverphat ra mot tra li khang nh vi mot dong cha thongtin cho message o, dong nay c goi la scan listing cho

message o.Neu khong co oi so c trao cho va POP3 server phat

ra mot tra li khang nh th tra li c cho la multi-line.Sau khi khi tao +OK , cho moi message trong maildrop, POP3server tra li vi mot dong cha thong tin cho messageo. Dong nay cung c goi la mot scan listing chomessage o .

Phu hp e n gian hoa viec phan tch cu phap, tatca cac POP3 server yeu cau dung mot nh dang cho scanlisting. Mot scan listing bao gom message number cua message

o, theo sau la mot khoang trang n va kch thc chnh xaccua message o bang he tam, khong yeu cau nhng g theosau message size trong scan listing .

Lu y: ay ngan can mot cach manh me s thcthi cac thong tin phu cung cap trong scan listing. Matkhac, ieu kien c ban luan sau , no cho phep clientphan tch cu phap cac message trong maildrop. Nhngmessage c anh dau xoa khong c liet ke .

- Cau tra li co the:+OK scan listing follows-ERR no such message

V du :C: LISTS: +OK 2 messages (320 octets)S: 1 120S: 2 200S: ....

C: LIST 2S: +OK 2 200...

C: LIST 3

S: -ERR no such message, only 2 messages in maildrop

RETR msg- oi so : Mot message-number (c yeu cau) no co thekhong tham khao en mot message c anh dau xoa.

- Gii han : Ch c cho trong trang thai TRASACTION- Discussion : Neu POP3 server phat ra mot tra li khang

nh, th tra li c trao la multi-line. Sau khi khi tao +OK ,


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POP3 server gi mot message tng ng vi message-numberc cho, mot cach can than e byte-stuff ky t cuoi cung(nh vi cac tra li multi-line) .

- Cau tra li co the:+OK message follows

-ERR no such messageV du :C: RETR 1S: +OK 120 octetsS: S: .

DELE msg- oi so : Mot message-number (c yeu cau) co thekhong tham khao en mot message c anh dau xoa.

- Gii han : Ch c cho trong trang thai TRANSACTION .

- Discussion : POP3 server anh dau xoa message o.Nhng tham khao sau o en message-number ket hp vimessage o cua mot lenh POP3 se sinh ra loi. POP3 serverkhong that s xoa message o cho en khi POP3 session i vaotrang thai UPDATE .

- Cau tra li co the:+OK message deleted-ERR no such message

V du :C: DELE 1S: +OK message 1 deleted

...C: DELE 2S: -ERR message 2 already deleted

NOOP- oi so: khong- Gii han : Ch c cho trong trang thai TRANSACTION- Discussion : POP3 server khong lam g het , no ch hoi

am vi mot tra li khang nh.- Cau tra li co the:

+OK

V du:C: NOOPS: +OK

RSET- oi so: khong- Gii han : Ch c cho trong trang thai TRANSACTION .


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- Discussion : Neu mot message nao o a c anhdau xoa bi POP3 server, chung c bo anh dauxoa(unmark ). Sau o POP3 server hoi am vi mot tra likhang nh.

- Cau tra li co the:

+OKV du :C: RSETS: +OK maildrop has 2 messages (320 octets)

V. Trang thai cap nhat (update)Khi client phat ra mot lenh QUIT t trang thai

TRANSACTION, POP3 session i vao trang thai UPDATE (lu y rangneu client phat ra mot lenh QUIT t trang thai AUTHORIZATION,POP3 session ket thuc nhng khong i vao trang thai UPDATE).

Neu POP3 session ket thuc v cac l do khac sau o mot

lenh QUIT c phat ra t client, POP3 session khong i vaotrang thai UPDATE va PHAI khong remove mot message naot maildrop o. QUIT

- oi so: khong- Gii han: khong- Discussion : POP3 server loai bo tat ca cac mesasage c

anh dau xoa t maildrop. Sau o no giai phong cac khoatruy cap loai tr (exclusive-access lock) tren maildrop o vacac reply ve phan tnh trang cua nhng thao tac nay. Sau oket noi TCP c ong lai.

- Cau tra li co the:+OK

V du :C: QUITS: +OK dewey POP3 server signing off (maildrop empty)

...C: QUITS: +OK dewey POP3 server signing off (2 messages left)

...VI. Cac lenh POP 3 chon la (optional POP3

commands)Nhng lenh POP3 c noi en tren phai c hotr bi s thc thi toi thieu cua POP3 server.

Cac lenh POP3 la chon c mo ta sau ay cho phepmot POP3 client t do hn trong viec ieu khien message, trongkhi van gi mot s thc thi POP3 server n gian.


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Lu y: So ghi chep khuyen khch nhng s th thi nhamho tr cho nhng lenh nay thay cho viec phat trientang them drop va scan listings. Thu gon, triet ly cua soghi nh la nham at mot s thong minh trong vai trocua client POP3 va khong cho server POP3.

TOP msg n- oi so: Mot message-number (c yeu cau) no co thekhong tham khao en mot message c anh dau xoa,va mot non-negative number (c yeu cau) .- Gii han : Ch c cho trong trang thai TRANSACTION- Discussion : Neu POP3 server phat ra mot tra li khang

nh, th tra li c trao la multi-line. Sau khi tao +OK , POP3server gi header cua message o, dong trong tach headerkhoi body, va sau o la so dong ch nh phan body cuamessage, nen can than e byte-stuff ky t cuoi cung (nh

vi tat ca cac tra li muti-line) .Chu y : Neu so dong c yeu cau bi POP3 clientln hn so dong trong body

th POP3 server gi toan bo message o .- Cau tra li co the:

+OK top of message follows-ERR no such message

V du :C: TOP 1 10S: +OKS: < POP3 server gi phan headers cua message, mot

dong trong, va 10 dong au tien cua phan body cuamessage o>S: ....

C: TOP 100 3S: -ERR no such message

UIDL [msg]- oi so: Mot message-number (tuy y) neu mot messagenumber c cho, no co the khong tham khao en motmessage c anh dau xoa.

- Gii han : Ch co the c cho trong trang thaiTRANSACTION .

- Discussion : Neu mot oi so c cho va POP3 serverphat ra mot tra li khang nh vi mot dong cha thongtin cho message o. Dong nay c goi la mot unique-idlisting cho message o.

Neu khong co oi so nao c cho va POP3 serverphat ra mot tra li khang nh th cau tra li c trao la


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multi-line. Sau khi khi tao OK cho moi message trong maildrop,POP3 server tra li vi mot dong cha thong tin cho messageo. Dong nay c goi la mot unique-id listing cho messageo.

Hp le e n gian hoa viec phan tch cu phap. Tatca cac server c yeu cau dung mot nh dang cho cacunique-id-listing. Mot unique-id-listing bao gom message numbercua message theo sau la mot khoang trang va unique-id cuamessage. Khong co thong tin khac theo sau unique-id trongunique-id-listing.

Unique-id cua mot message la mot chuoi xac nhserver tuy y, bao gom nhng ky t trong pham vi 0x21 en0x7E, no nh danh mot message ben trong mot maildrop la duynhat va no gi nh vay trong thi gian hoi ngh. Server sekhong bao gi dung lai mot unique-id trong mot maildrop a

cho. Nhng message c anh dau xoa khong cliet ke.

- Cau tra li co the+OK unique-id listing follows-ERR no such message

V du :C: UIDLS: +OKS: 1 whqtswO00WBw418f9t5JxYwZS: 2 QhdPYR:00WBw1Ph7x7

S: ....C: UIDL 2S: +OK 2 QhdPYR:00WBw1Ph7x7...

C: UIDL 3S: -ERR no such message, only 2 messages in maildrop

APOP name digest- oi so : Mot chuoi nh danh mot mailbox va motchuoi MD5 digest ( yeu cau ca hai).

- Gii han : Ch co the c cho trong trang thaiAUTHORIZATION sau khi POP3 chao hoi.

- Discussion : Thng th, moi POP3 session bat au vimot s trao oi USER/PASS, no dan en mot password ac taserver/user-id c gi len mang . Nhng s thc thi cua POP3client ket noi en POP3 server theo mot quy tac c ban ekiem tra mail mi. Hn na khoang thi gian khi tao motPOP3 session theo quy tac la nam phut. Luc o kha nang b


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anh cap password rat ln. oi hoi phai co mot thay oitrong phng thc xac nhan cung cap ca s xac nhan vaxem lai s bao ve, nhng no khong bao gom viec gi motpasssword khong c ma hoa len mang. Lenh APOP cung capchc nang nay.

Mot POP3 server thc thi lenh APOP no se a mot donganh dau thi gian vao trong banner greeting cua no. POP3client ghi nh dong anh dau thi gian nay va sau o phatra lenh APOP.

Tham so name giong nh tham so name trong lenh USERtham so digest cb tnh toan bang cach ap dung giai thuatMD5 [RFC1321] cho mot chuoi cha moc thi gian (nam trongdau ngoac tron) theo sau la mot share secret. Share secret lamot chuoi ch e nhan biet client va server.

Tham so digest la mot gia tr 16-octet no c g theoformat cua he hex.

Khi mot server POP3 nhan c mot lenh APOP, no kiemtra digest. Neu digest ung, POP3 server phat ra mot tra likhang nh va POP3 session i vao trang thai TRANSACTION.Ngc lai no phat ra mot tra li phu nh va POP3 sessionvan gi trang thai AUTHORIZATION

- Cau tra li co the:+OK maildrop locked and ready

-ERR permission deniedV du :

S: +OK POP3 server ready

C: APOP mrose c4c9334bac560ecc979e58001b3e22fbS: +OK maildrop has 1 message (369 octets)Trong v du nay share secret la chuoi `tan-staaf'. Giai thuat

MD5 c ap dung cho chuoitanstaaf

no sinh ra mot gia tr digestc4c9334bac560ecc979e58001b3e22fb

VI. Tom tac cac lenh POP3A. Cac lenh can phai co :

USER name co hieu lc trong trang thai

AUTHORIZATIONPASS stringQUIT

STAT co hieu lc trong trang thaiTRANSACTION

LIST [msg]RETR msg


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DELE msgNOOPRSET

QUIT co hieu lc trong trang thai UPDATE

* Cac lenh POP3 chon la:APOP name digest co hieu lc trong trang thai

AUTHORIZATION TOP msg n co hieu lc trong trang

thai TRANSACTIONUIDL [msg}

* Cac reply POP3 :+OK-ERR

LU Y : Vi s chap nhan cac lenh STAT, LIST, va UIDL ,reply ma POP3 server gi cho cac lenh ch mang y ngha"+OK" va "-ERR". Nhng text xuat hien sau trply nay se cclient pht l.

B. Cac chuan truyen khac :Ngoai hai chuan truyen tren, Mail con co cac chuan

truyen khac nh :- MAIP : Chuan MAPI da tren nen tang mo hnh COM.

Chuan nay co rat nhieu chi tiet, nhieu e muc, ham,

interface, Object...Trong chuan MAPI, tat ca nhng thanh phan bo phan

eu c xem nh la nhng oi tng, muon thao tac vinhng bo phan o, eu phai theo cach thc truy nhapvao mot Object, sau o mi co the s dung cac methodcua Interface ma Objectt tng ng ho tr. V du nh ngay cathong iep cung c xem la mot oi tng, o laMessage Object.

- ESMTP (Extender SMTP) - Nghi thc m rong SMTPSMTP co mot han che gay kho khan ln trong viec

truyen nhan mail la gii han toi a kch thc noi dungmot bc mail ch la 128KB.Ngay nay noi dung cac bc mailkhong ch la dang van ban n thuan ma con bao gomhnh anh, am thanh va nhieu loai d lieu khac na, giihan 128KB tr nen qua nho.

Do vay ngi ta a cai tien chuan SMTP thanh motchuan m rong mi goi la ESMTP.


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Chuan nay cho phep tang kch thc mail, no athem t khoa SIZE=nnnnnnn sau lenh khi ong cuoc giaodch, nh o ta co the tang gii han kch thc cua maillen tren 1MB, u e cha them vao cac am thanh, hnhanh

e biet xem Server MTA co theo chuan ESMTP haykhong, thay v dung lenh HELLO au mot cuoc giao dch,Client MTA dung lenh mi EHLO, neu Server MTA co trang b,no se tra ve ma thanh cong la 250.

Hien nay hau nh chuan ESMTP a thay the chuanSMTP a so cac he thong.

- X.400 : Chuan X.400 la mot bo phan cua cac chuan OpenSystems Interconnection ( OSI ) ve truyen dan thong iepien t ( electronic Messaging Handling System - MHS ) cphat trien bi to chc ien thoai va Truyen thong quoc

te ( Comite Consultatif International de Telegraphique etTelephonique - CCITT ), c xay dng tren viec tham khaomo hnh 7 lp cua OSI va cac protocol c nh ngha biTo chc tieu chuan quoc te ( International Organization forStandardization - ISO )

-

*. Thong iep theo chuan X.400 :Mot thong iep X.400 co 2 thanh phan : Phan phong b

cha thong tin can thiet e phan phoi mot thong iepva phan noi dung cha thong tin can truyen. Phan phong bc dung bi MTA va phan Noi dung c dung bi UA.

Phan Noi dung thong tin to chc theo dang IPM ( InterpersonalMessage : Dang th tn ca nhan rieng t ) bao gom 2 phancach biet nhau : Heading va Body. Heading bao gom cacthong tin nh a ch ni i va en, cho biet loai th hoacyeu cau phan hoi.Body cha noi dung can gi.

Cac tai lieu ve X.400 ra i nam 1984, va c goi la "red book " ( v chung co ba mau o ). c tu chnh va in lanhai vao nam 1988 va c goi la " blue book " ( v chung coba xanh ).

tim hieu ve giao thuc smtp

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