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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…

E-mail

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 harry@sparcs.org, harry@sparcs.net, har-ry@143.248.234.102 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 ‘harry@sparcs.kaist.ac.kr’.

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 webmas-ter@sparcs.org 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 wheel-seminar@sparcs.org 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 harry@gmail.com, all mails sent to harry@sparcs.org will be delivered to harry@gmail.com, in fact.

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Settings

• Alias– harry : harry@gmail.com

• /home/harry/.forward– harry@gmail.com

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Questions?

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Thank you!