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Postfix is a powerful Mail Transfer Agent (MTA) and the de facto standard.


As only one MTA can be installed at the same time on a system, you might be required to unmerge an installed MTA. The package manager will report a block when another MTA is still installed. You can resolve this block by manually unmerging the old mail server. For example you can remove mail-mta/ssmtp (which might have been installed as the default when a program requested a mail server to be installed) with this command:

root #emerge --ask -C ssmtp


mail-mta/postfix has several USE flags that may be desired for certain bigger setups. As this article aims at installing and configuring a basic Postfix setup, none of them will be required initially.

USE flag (what is that?) Default Recommended Description
berkdb Yes Add support for sys-libs/db (Berkeley DB for MySQL)
cdb No Add support for the CDB database engine from the author of qmail
doc No Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally
dovecot-sasl No Enable net-mail/dovecot protocol version 1 (server only) SASL implementation
hardened No Yes Activate default security enhancements for toolchain (gcc, glibc, binutils)
ldap Yes Add LDAP support (Lightweight Directory Access Protocol)
ldap-bind No Adds support for binding to LDAP backend using dev-libs/cyrus-sasl
mbox No Add support for mbox (/var/spool/mail) style mail spools
memcached No Adds support for using net-misc/memcached for lookup tables
mysql No Add mySQL Database support
nis No Support for NIS/YP services
pam No Add support for PAM (Pluggable Authentication Modules) - DANGEROUS to arbitrarily flip
postgres No Yes Add support for the postgresql database
sasl No Yes Add support for the Simple Authentication and Security Layer
selinux No  !!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur
sqlite No Add support for sqlite - embedded sql database
ssl Yes Add support for Secure Socket Layer connections
vda No Yes Adds support for virtual delivery agent quota enforcing
root #emerge --ask postfix


Fully Qualified Domain Name (FQDN)

Though not entirely related, for a MTA to function properly, it is imperative that its hostname is set up correctly. Under Gentoo /etc/conf.d/hostname and /etc/conf.d/net are the files responsible for this. In this example, the mail server is named foo on the domain

FILE /etc/conf.d/net Setup domain name
FILE /etc/conf.d/hostname Setup hostname
Do not use just because it may be externally known as such. Use the actual name of the system.

Verifying that the FQDN is setup properly for the domain.

user $hostname --fqdn

If for any reason the FQDN cannot be set properly, Postfix needs to be told what its FQDN is. Otherwise leave it at its commented out default.

FILE /etc/postfix/ Inform Postfix of its FQDN
myhostname =
mydomain =

If you wish to have your mail appear as coming from instead of then

FILE /etc/postfix/ specify your own FQDN
myhostname =
mydomain =

Trust and Relay

This one is a really important thing to get right. By default, a Postfix installation is pretty tight, only allowing users on the same subnet as the mail server to relay email through Postfix. If this gets messed around with, it can potentially open the door to all users from anywhere. This is called an open relay and is begging for abuse by spam merchants, likely resulting in your domain to be quickly blacklisted. This defeats the purpose of setting up a personal mail server, if nobody will talk or listen to it.

There are means and ways, like SMTP Authentication, that allow you to secure access to your mail server even further. Depending on the trustworthiness of the users connected to the local network, it might be beneficiary to restrict access even for machines within the own subnet. This also has the benefit of not letting potentially compromised machines in the local network abuse the mail system, but entails additional configuration. To only allow the mail server itself to relay email without authentication, make a change to

FILE /etc/postfix/ Trust no-one
mynetworks_style = host
Internal servers of course don't have to to use this server to relay, they can still use ssmtp to send monitoring information if needed.

Address extensions

Address extensions allow you to encode additional information besides the recipient in a valid email address. The recipient is separated from the additional information usually by a + character, but it is configurable. To enable support for address extensions, edit your

FILE /etc/postfix/ Set a delimiter to enable address extensions
# ADDRESS EXTENSIONS (e.g., user+foo)
recipient_delimiter = +

The way this works is, when trying to deliver a message to, Postfix will try to deliver the message to testuser+spam first, if no such user is found, it will be delivered to testuser, the part of the email address before the delimiter. This feature can be quite useful for sites that require email address registration. Signing up with allows to easily filter and trace where a message originated from. If for example some unsolicited mail was delivered to that address, it likely comes from somesite. Even better filtering of unsolicited email can be achieved by using Spamassassin or AMaViS.

Miscellaneous configuration


When Postfix completes merging and the mailbox USE flag is set, a home_mailbox directive is added at the bottom of the file. To make future updates easier, it's a good idea to move the home_mailbox = .maildir/ to its appropriate location in the file.

For testing purposes, the following two features can be temporarily enabled:

Soft bounce

Soft bounce decreases the chances of endless bounce loops caused by an invalid email setup. To enable soft bouncing, add this to your

FILE /etc/postfix/ Soft Bounce
soft_bounce = yes

Verbose SMTP

This often hides problems in a mountain of logs and should only be done as a last resort. The default logging provides enough information to point you in the right direction.

Before testing the basic mail server setup, the verbose flag of the smtp server can be enabled by adding a -v to the smtpd daemon invocation in

FILE /etc/postfix/ Verbose smtpd
# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (yes)   (never) (100)
# ==========================================================================
smtp      inet  n       -       n       -       -       smtpd -v

That rounds up basic configuration. Postfix offers a vast amount of other features, including virtual domains and users, that exceed the current scope of this article.

Starting Postfix

Before starting Postfix for the first time, the local alias database has to be compiled. If this is not done, Postfix may appear to have started normally, but won't work and the log (usually found in /var/log/mail.log) will be spammed with errors:

Mar 16 11:40:32 foo postfix/smtpd[18923]: fatal: open database /etc/mail/aliases.db: No such file or directory

The alias database contains default local accounts required by various RFCs and common internet practice, as well as some pseudo accounts. Simply run the newaliases command to generate the database:

root #newaliases

Now it is time to start postfix for the very first time.

root #/etc/init.d/postfix start

It can be very useful to monitor the mail log file using tail -f. A successful start looks like this:

Nov 23 15:26:42 foo postfix/postfix-script[13433]: starting the Postfix mail system
Nov 23 15:26:42 foo postfix/master[13434]: daemon started -- version 2.8.4, configuration /etc/postfix

Testing Postfix

For the lay person, email your self, and don't forget to check the spam box. (if your email were to happen to be

root #echo "test" | sendmail

Now that Postfix is running properly, it should accept connections on port 25, the default SMTP port, and send email anywhere in the world. As SMTP is a simple plain-text protocol, you can easily send email manually using a telnet client. Replace the example address <(username)@(validdomain).(tld)> with a real email address to see it work. This is an example SMTP conversation with the parts the client (in this case that is you) sends are highlighted in blue color:

user $telnet 25

Connected to
Escape character is '^]'.
220 ESMTP Postfix
HELO localhost
250 2.1.0 Ok
RCPT TO: <(username)@(validdomain).(tld)>
250 2.1.5 Ok
354 End data with <CR><LF>.<CR><LF>
Subject: Test email

Testmail to ensure Postfix is working.
250 2.0.0 Ok: queued as 6705C20E32
221 2.0.0 Bye

Connection closed by foreign host.

Looking at /var/log/mail.log it can be verified that the message got properly relayed:

Nov 23 16:13:02 foo postfix/smtpd[28494]: connect from[]
Nov 23 16:13:49 foo postfix/smtpd[28494]: 6705C20E32:[]
Nov 23 16:13:51 foo postfix/cleanup[28508]: 6705C20E32: message-id=<>
Nov 23 16:13:51 foo postfix/qmgr[28490]: 6705C20E32: from=<>, size=314, nrcpt=1 (queue active)
Nov 23 16:13:52 foo postfix/smtp[28510]: 6705C20E32: to=<(username)@(validdomain).(tld)>, relay=mail.(validdomain)(.tld)[]:25, ⏎
delay=19, delays=18/0.02/0.37/0.32, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as 469A684F8)
Nov 23 16:13:52 foo postfix/qmgr[28490]: 6705C20E32: removed
Nov 23 16:13:54 foo postfix/smtpd[28494]: disconnect from[]

Performing the same test from a different host should fail, as it is untrusted:

user $telnet 25

Connected to
Escape character is '^]'.
220 ESMTP Postfix
HELO localhost
250 2.1.0 Ok
RCPT TO: <(username)@(validdomain).(tld)>
454 4.7.1 <(username)@(validdomain).(tld)>: Relay access denied
221 2.0.0 Bye

Connection closed by foreign host.

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