s ystem p rogrammers' a ssociation for r esearching c omputer s ystems popular mtas exim &...
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Popular MTAsEXIM & POSTFIX
SPARCS 10 이대근 (harry)
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MTA
Mail Transfer Agent
Message Transfer Agentor
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Let’s recall…
MTA MTA
MUA (ex: outlook express)MUA
그냥 새
MDA : Mail 우편함
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With MTA you can…
• Send and receive an email, of course– To users of your machine, without ISP– To other mail servers, you need connection to internet
• Fetch emails from POP3 server– using fetchmail
• Receive emails in right place– Using procmail
• Get messages from some programs via e-mail– Log files or security warnings can be delivered to your email
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A Lot of MTAs
AndQmail, Courier, Smail, MMDF…
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EXIMEXperimental Internet Mailer
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EXIM
• One of the most popular MTAs• Default MTA for Ubuntu• SPARCS server
• GPL• Flexible, extensible• Good compatibility with Sendmail
• Latest stable release: 4.72 (2010/06/03)
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How EXIM delivers mails?
Internet
SMTP(25)Daemon
Mail server
SpoolReceiver
Queue runner
DeliveryRemoteDelivery
LocalDelivery Mailbox
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Message ID
1OROMT-0003j0-6G
The time at which the message started to be received. The number of sec-onds since the start of the epoch.
Time Process IDID of the process which received the message.
TimeFractional part of the time of recep-tion. The unit may be 1/2000 sec, 1/1000 sec, 1/200 sec or 1/100 sec.
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Command line options
# exim [options] [arguments]
––helpDisplays help message
–bdRuns exim as a daemon, awaiting incoming SMTP connections from all available interfaces. Usually used with option –q.
–qStarts one queue runner process. Time specifications start queue runner periodically. (–q30m for starting every 30 minutes)
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Command line options
# exim [options] [arguments]
–Mc <message id> <message id> …Deliver messages in turn. Usually called internally by queue runner.
–C <filelist>Find configuration files in <filelist> and apply them instead of de-fault configuration file specified by CONFIGURE_FILE.
–bP <option name> <option name> …Print the current configuration to standard output.
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Let’s see SPARCS server
[21:56:58]harry@sparcs:~$ ps aux | grep exim102 2563 0.0 0.0 13344 1332 ? Ss Jul01 0:02 /usr/sbin/exim4 -bd -q30mRoot 17964 0.0 0.2 13588 3680 ? S 18:14 0:00 /usr/sbin/exim4 -Mc 1OXW93-0004fL-QH102 17966 0.0 0.1 13588 2056 ? S 18:14 0:00 /usr/sbin/exim4 -Mc 1OXW93-0004fL-QH102 17976 0.0 0.0 13352 896 ? S 18:14 0:00 /usr/sbin/exim4 -bd -q30m
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Configuring EXIM
• EXIM configuration file is divided into 6 parts– ACL: Access control list for controlling incoming SMTP mails– Authenticators: Settings for authenticator drivers– Routers: Determines how the messages is to be delivered– Transports: Defines the mechanisms how the messages are to be
copied– Retry: Rules for use when the message cannot be delivered imme-
diately– Rewrite: Global address rewriting rules– Local_scan: Private options for local_scan() function
Difficult?
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/etc/exim4/update-exim4.conf.conf
[21:56:58]harry@sparcs:/etc/exim4$ cat update-exim4.conf.conf# /etc/exim4/update-exim4.conf.conf## Edit this file and /etc/mailname by hand and execute update-exim4.conf# yourself or use 'dpkg-reconfigure exim4-config'## Please note that this is _not_ a dpkg-conffile and that automatic changes# to this file might happen. The code handling this will honor your local# changes, so this is usually fine, but will break local schemes that mess# around with multiple versions of the file.## update-exim4.conf uses this file to determine variable values to generate# exim configuration macros for the configuration file.## Most settings found in here do have corresponding questions in the# Debconf configuration, but not all of them.## This is a Debian specific file
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/etc/exim4/update-exim4.conf.conf
dc_eximconfig_configtype='internet'dc_other_hostnames='sparcs.org;sparcs.net;143.248.234.102'dc_local_interfaces=''dc_readhost=''dc_relay_domains=''dc_minimaldns='false'dc_relay_nets=''dc_smarthost=''CFILEMODE='644'dc_use_split_config='true'dc_hide_mailname=''dc_mailname_in_oh='true'dc_localdelivery='maildir_home'
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/etc/exim4/update-exim4.conf.conf
dc_eximconfig_configtype='internet'
dc_eximconfig_configtype : The main configuration type.
‘local’: Mails are sent and received between the accounts of local machine‘internet’: Configure as a general email server connected to internet‘satellite’: Sends mail to another machine(smarthost)‘smarthost’: Intermediates email
Sets macro DC_eximconfig_configtype.
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/etc/exim4/update-exim4.conf.conf
dc_other_hostnames='sparcs.org;sparcs.net;143.248.234.102'
dc_other_hostnames : List of domains of mails that the server will finally accept
Multiple values can be set, separated by colon(:).
Mails delivered to [email protected], [email protected], [email protected] will be passed from daemon process to receiver process.
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/etc/exim4/update-exim4.conf.conf
dc_local_interfaces=''
dc_local_interfaces : List of IPs for daemon to listen on
Multiple values can be set, separated by colon(:).
Empty string means all interfaces.
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/etc/exim4/update-exim4.conf.conf
CFILEMODE='644'
CFILEMODE : The octal file mode of the generated file
Sets the mode of the files that are generated by update-exim4.conf.
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/etc/exim4/update-exim4.conf.conf
dc_use_split_config='true'
dc_use_split_config : Defines whether it uses split configuration files
‘true’: Uses multiple files below /etc/exim4/conf.d‘false’: Uses single file /etc/exim4/exim4.conf.template
dc_localdelivery='maildir_home'
dc_local_delivery : Name of default transport directory
‘’ or ‘mail_spool’: Mails are delivered to spool by default‘maildir_home’: Mails are delivered to ~/Maildir/ by default
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Update configuration
# update-exim4.conf –d /etc/exim4 –o /etc/exim4/exim4.conf
Automatically generates configuration files.
# /etc/init.d/exim4 restart
Restarts the daemon with new configuration.
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Log files
• /var/log/exim4/mainlog
• /var/log/exim4/rejectlog
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POSTFIX
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POSTFIX
• One of the most popular MTAs
• IBM Public License(free)
• Secure alternative to Sendmail• Able to handle large amounts of emails
• Latest stable release: 2.7.1 (2010/06/08)
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Installation
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/etc/postfix/main.cf
[21:56:58]harry@sparcs:/etc/postfix$ cat main.cf# See /usr/share/postfix/main.cf.dist for a commented, more complete version
# Debian specific: Specifying a file name will cause the first# line of that file to be used as the name. The Debian default# is /etc/mailname.myorigin = /etc/mailname
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)biff = no
# appending .domain is the MUA's job.append_dot_mydomain = no
# Uncomment the next line to generate "delayed mail" warnings#delay_warning_time = 4h
readme_directory = no
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/etc/postfix/main.cf
# TLS parameterssmtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pemsmtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.keysmtpd_use_tls=yessmtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scachesmtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for# information on enabling SSL in the smtp client.
myhostname = sparcsalias_maps = hash:/etc/aliasesalias_database = hash:/etc/aliasesmydestination = sparcs.org, sparcs.net, localhost.localdomain, , localhostrelayhost = mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128mailbox_size_limit = 0recipient_delimiter = +inet_interfaces = all
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/etc/postfix/main.cf
# Debian specific: Specifying a file name will cause the first# line of that file to be used as the name. The Debian default# is /etc/mailname.myorigin = /etc/mailname
myorigin : Specifies the domain that appears in mail that posted on this machine.
/etc/mailname has sparcs.kaist.ac.kr in its first line, so specifying myorigin = /etc/mailname makes the sender of the mails outgoing from this machine like ‘[email protected]’.
myorigin = $mydomain is one of the most generally used set-tings.
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/etc/postfix/main.cf
mynetworks_style = subnet
mynetworks_style : Specifies what kinds of clients to relay mail from.
host: Forwards mails from only the local machinesubnet: Forwards mail from the clients in the same subnetwork as the machineclass: Forwards mail from the clients in the same class as the ma-chine
If mynetworks_style is not set, you should specify the mynetworks list by hand.
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/etc/postfix/main.cf
mydestination = sparcs.org, sparcs.net, localhost.localdomain, , localhost
mydestination : Specifies what domains this server will finally accept
Multiple values can be set, separated by commas(,).
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/etc/postfix/main.cf
relayhost =
relayhost : Specifies the delivery method
(empty string): Deliver the mail directly to the internet$mydomain: Deliver mails via local mail server
inet_interfaces = all
inet_interfaces : Specifies what interfaces that daemon should listen on
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Update configuration
# postfix reload# /etc/init.d/postfix restart
Restarting postfix daemon will apply your new settings
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Log files
• /var/log/mail.log
• /var/log/mail.info• /var/log/mail.err• /var/log/mail.warn
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ALIASES & FORWARDING
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Aliases
• Alias is a way to use a virtual mail account– If webmaster is an alias of harry, messages sent to [email protected] will be redirected to harry’s mailbox.
• Alias is an easy way to configure mailing list– If wheel-seminar is aliases of all members who participates in
wheel seminar, messages sent to [email protected] will be redirected to their mailboxes.
• MTAs automatically reads alias database when the delivery process starts and deliver messages according to it.
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/etc/aliases
• <alias> : <actual name>– webmaster : harry
• <alias> : :include:<file name>– wheel-seminar : :include:/SPARCS/mail/aliases.d/wheel-seminar– Files is just a list of usernames separated by newlines.
• We have a good tool: edalias
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newaliases
• MTAs read /etc/aliases.db, not /etc/aliases.• You have to update database file after editing aliases files.
• # newaliases
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Forwarding
• Pass messages to other mail addresses
• If harry forwards his mails to [email protected], all mails sent to [email protected] will be delivered to [email protected], in fact.
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Settings
• Alias– harry : [email protected]
• /home/harry/.forward– [email protected]
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Questions?
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Thank you!