Postfix (简体中文)

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翻译状态：本文是 Postfix 的翻译。上次翻译日期：2018-12-06。如果英文版本有所更改，则您可以帮助同步翻译。

Postfix 是邮件传输代理软件。按照其 官方网站的说法:

attempts to be fast, easy to administer, and secure, while at the same time being sendmail compatible enough to not upset existing users. Thus, the outside has a sendmail-ish flavor, but the inside is completely different.

快速、管理简单、安全， 同时足够兼容Sendmail (简体中文)，从而不会影响现有用户。 因此，从外面看是sendmail-ish风格，但内部是完全不同的。

本文基于 邮件服务器。 本文的目标是设置Postfix并解释基本配置文件的功能。 这里有两种交付方式的设置说明：本地系统用户方式 和 虚拟用户方式。

安装

安装 软件包 postfix。

配置

请参照软件开发者提供的： Postfix Basic Configuration 基础配置项. 默认的配置文件位于/etc/postfix 。 其中两个非常重要的文件是:

• master.cf, 定义了启用哪些Postfix服务以及客户端如何连接它们, 请参照 master(5)
• main.cf, 主配置文件，请参照 postconf(5)（英文）

配置文件更改过后需要 重新加载 主服务 postfix.service。

别名 Aliases

请参照在线 man 文件： aliases(5)。

别名配置文件： /etc/postfix/aliases。你可以在这个文件里指定别名 (有时候也被称为 forwarders ) 。

您需要将发往“root”的所有邮件映射到另一个帐户，因为以root身份阅读邮件不是一个好主意。

将下面这行取消注释，并且把 you 替换成你要使用的真实账户。

root: you

一旦你完成了对 /etc/postfix/aliases 的编辑， 你就需要运行下面的 postalias 命令:

postalias /etc/postfix/aliases

对于以后的更改，您可以使用:

newaliases

提示： 或者，你也可以为 root 用户创建这个文件 ~/.forward, 例如 /root/.forward。 指定将root的邮件转发到哪个用户, 例如 user@localhost。

/root/.forward

user@localhost

系统本地用户邮件(Local mail)

要仅向本地系统用户（也就是/etc/passwd中存在的用户）发送邮件，请更新配置文件：/etc/postfix/main.cf中的以下配置行（取消注释，更改或添加）:

myhostname = localhost
mydomain = localdomain
mydestination = $myhostname, localhost.$mydomain, $mydomain
inet_interfaces = $myhostname, localhost
mynetworks_style = host
default_transport = error: outside mail is not deliverable

所有其他设置维持不变。 完成上面这个配置后，你可能还想配置一些#别名 Aliases参数，然后#启动 Postfix。

虚拟用户邮件(Virtual mail)

虚拟用户邮件的邮件账户不存储在本地系统的(/etc/passwd文件中。可以配合数据库完成对用户账户的存储。

请参见 Virtual user mail system with Postfix, Dovecot and Roundcube (简体中文) 那是一个如何设置的详细介绍。

检查配置 Check configuration

运行postfix check 命令来完成配置检查。它会输出所有你在配置文件中可能写错的东西。

运行postconf命令可以查看所有的配置。运行postconf -n命令可以查看与默认配置的区别。

启动 Postfix

注意： 即使你没有设置任何#别名 Aliases，也需要至少运行一次newaliases命令才能让 Postfix 正常运行。

启动 postfix.service 服务。

TLS

警告： If you deploy TLS, be sure to follow weakdh.org's guide to prevent FREAK/Logjam. Since mid-2015, the default settings have been safe against POODLE. For more information see Server-side TLS.

You need to obtain a certificate.

For more information, see Postfix TLS Support.

Secure SMTP (sending)

By default, Postfix/sendmail will not send email encrypted to other SMTP servers. To use TLS when available, add the following line to main.cf:

/etc/postfix/main.cf

smtp_tls_security_level = may

要强制使用TLS (这种情况下如果远程服务器不支持的话会导致失败), 只需要把 may 变更为 encrypt 就行了。 值得注意的是，如果此邮件服务是一个公开的服务(相对于企业内部服务，不对公网提供服务的那种)时，这样的做法会违反 RFC:2487 ，所以请慎重考虑。

Secure SMTP (receiving)

By default, Postfix will not accept secure mail.

To enable STARTTLS over SMTP (port 587, the proper way of securing SMTP), add the following lines to main.cf

/etc/postfix/main.cf

smtpd_tls_security_level = may
smtpd_tls_cert_file = /path/to/cert.pem
smtpd_tls_key_file = /path/to/key.pem

In master.cf, find and uncomment the following lines to enable the service on that port with the correct settings:

/etc/postfix/master.cf

submission inet n       -       n       -       -       smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_tls_auth_only=yes
  -o smtpd_reject_unlisted_recipient=no
#  -o smtpd_client_restrictions=$mua_client_restrictions
#  -o smtpd_helo_restrictions=$mua_helo_restrictions
#  -o smtpd_sender_restrictions=$mua_sender_restrictions
  -o smtpd_recipient_restrictions=
  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING

The smtpd_*_restrictions options remain commented because $mua_*_restrictions are not defined in main.cf by default. If you do decide to set any of $mua_*_restrictions, uncomment those lines too.

If you need support for the deprecated SMTPS port 465, also follow the next section.

SMTPS (port 465)

The deprecated method of securing SMTP is using the wrapper mode which uses the system service smtps as a non-standard service and runs on port 465.

To enable it, uncomment the following lines in master.cf:

/etc/postfix/master.cf

smtps     inet  n       -       n       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_reject_unlisted_recipient=no
#  -o smtpd_client_restrictions=$mua_client_restrictions
#  -o smtpd_helo_restrictions=$mua_helo_restrictions
#  -o smtpd_sender_restrictions=$mua_sender_restrictions
  -o smtpd_recipient_restrictions=
  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING

The rationale surrounding the $smtpd_*_restrictions lines is the same as above.

After this, verify that these lines are in /etc/services:

smtps 465/tcp # Secure SMTP
smtps 465/udp # Secure SMTP

If they are not there, go ahead and add them (replace the other listing for port 465). Otherwise Postfix will not start and you will get the following error:

postfix/master[5309]: fatal: 0.0.0.0:smtps: Servname not supported for ai_socktype

Tips and tricks

Blacklist incoming emails

Manually blacklisting incoming emails by sender address can easily be done with Postfix.

Create and open /etc/postfix/blacklist_incoming file and append sender email address:

user@example.com REJECT

Then use the postmap command to create a database:

# postmap hash:blacklist_incoming

Add the following code before the first permit rule in main.cf:

smtpd_recipient_restrictions = check_sender_access hash:/etc/postfix/blacklist_incoming

Finally restart postfix.service.

Hide the sender's IP and user agent in the Received header

This is a privacy concern mostly, if you use Thunderbird and send an email. The received header will contain your LAN and WAN IP and info about the email client you used. (Original source: AskUbuntu) What we want to do is remove the Received header from outgoing emails. This can be done by the following steps:

Add the following line to main.cf:

smtp_header_checks = regexp:/etc/postfix/smtp_header_checks

Create /etc/postfix/smtp_header_checks with this content:

/^Received: .*/     IGNORE
/^User-Agent: .*/   IGNORE

Finally, restart postfix.service.

Postfix in a chroot jail

Postfix is not put in a chroot jail by default. The Postfix documentation [1] provides details about how to accomplish such a jail. The steps are outlined below and are based on the chroot-setup script provided in the Postfix source code.

First, go into the master.cf file in the directory /etc/postfix and change all the chroot entries to 'yes' (y) except for the services qmgr, proxymap, proxywrite, local, and virtual

Second, create two functions that will help us later with copying files over into the chroot jail (see last step)

CP="cp -p"

cond_copy() {
  # find files as per pattern in $1
  # if any, copy to directory $2
  dir=`dirname "$1"`
  pat=`basename "$1"`
  lr=`find "$dir" -maxdepth 1 -name "$pat"`
  if test ! -d "$2" ; then exit 1 ; fi
  if test "x$lr" != "x" ; then $CP $1 "$2" ; fi
}

Next, make the new directories for the jail:

set -e
umask 022

POSTFIX_DIR=${POSTFIX_DIR-/var/spool/postfix}
cd ${POSTFIX_DIR}

mkdir -p etc lib usr/lib/zoneinfo
test -d /lib64 && mkdir -p lib64

Find the localtime file

lt=/etc/localtime
if test ! -f $lt ; then lt=/usr/lib/zoneinfo/localtime ; fi
if test ! -f $lt ; then lt=/usr/share/zoneinfo/localtime ; fi
if test ! -f $lt ; then echo "cannot find localtime" ; exit 1 ; fi
rm -f etc/localtime

Copy localtime and some other system files into the chroot's etc

$CP -f $lt /etc/services /etc/resolv.conf /etc/nsswitch.conf etc
$CP -f /etc/host.conf /etc/hosts /etc/passwd etc
ln -s -f /etc/localtime usr/lib/zoneinfo

Copy required libraries into the chroot using the previously created function cond_copy

cond_copy '/usr/lib/libnss_*.so*' lib
cond_copy '/usr/lib/libresolv.so*' lib
cond_copy '/usr/lib/libdb.so*' lib

And do not forget to reload Postfix.

DANE (DNSSEC)

Resource Record

警告： This is not a trivial section. Be aware that you make sure you know what you are doing. You better read Common Mistakes before.

DANE supports several types of records, however not all of them are suitable in Postfix.

Certificate usage 0 is unsupported, 1 is mapped to 3 and 2 is optional, thus it is recommendet to publish a "3" record. More on Resource Records.

Configuration

Opportunistic DANE is configured this way:

/etc/postfix/main.cf

smtpd_use_tls = yes
smtp_dns_support_level = dnssec
smtp_tls_security_level = dane

/etc/postfix/master.cf

dane       unix  -       -       n       -       -       smtp
  -o smtp_dns_support_level=dnssec
  -o smtp_tls_security_level=dane

To use per-domain policies, e.g. opportunistic DANE for example.org and mandatory DANE for example.com, use something like this:

/etc/postfix/main.cf

indexed = ${default_database_type}:${config_directory}/

# Per-destination TLS policy
#
smtp_tls_policy_maps = ${indexed}tls_policy

# default_transport = smtp, but some destinations are special:
#
transport_maps = ${indexed}transport

transport

example.com dane
example.org dane

tls_policy

example.com dane-only

注意： For global mandatory DANE, change smtp_tls_security_level to dane-only. Be aware that this makes Postfix tempfail (respond with a 4.X.X error code) on all deliveries that do not use DANE at all!

Full documentation is found here.

Extras

• PostfixAdmin — A web-based administrative interface for Postfix.

http://postfixadmin.sourceforge.net/ || postfixadmin

Postgrey

Postgrey can be used to enable greylisting for a Postfix mail server.

Installation

Install the postgrey package. To get it running quickly edit the Postfix configuration file and add these lines:

/etc/postfix/main.cf

smtpd_recipient_restrictions =
  check_policy_service inet:127.0.0.1:10030

Then start/enable the postgrey service. Afterwards, reload the postfix service. Now greylisting should be enabled.

Configuration

Configuration is done via editing the postgrey.service file. First copy it over to edit it.

# cp /usr/lib/systemd/system/postgrey.service /etc/systemd/system/

Whitelisting

To add automatic whitelisting (successful deliveries are whitelisted and do not have to wait any more), you could add the --auto-whitelist-clients=N option and replace N by a suitably small number (or leave it at its default of 5).

...actually, the preferred method should be the override:

cat /etc/systemd/system/postgrey.service.d/override.conf

[Service]
ExecStart=
ExecStart=/usr/bin/postgrey --inet=127.0.0.1:10030 \
       --pidfile=/run/postgrey/postgrey.pid \
       --group=postgrey --user=postgrey \
       --daemonize \
       --greylist-text="Greylisted for %%s seconds" \
       --auto-whitelist-clients

To add your own list of whitelisted clients in addition to the default ones, create the file /etc/postfix/whitelist_clients.local and enter one host or domain per line, then restart postgrey.service so the changes take effect.

Troubleshooting

If you specify --unix=/path/to/socket and the socket file is not created ensure you have removed the default --inet=127.0.0.1:10030 from the service file.

For a full documentation of possible options see perldoc postgrey.

SpamAssassin

This section describes how to integrate SpamAssassin.

SpamAssassin stand-alone generic setup

注意： If you want to combine SpamAssassin and Dovecot Mail Filtering, ignore the next two lines and continue further down instead.

Edit /etc/postfix/master.cf and add the content filter under smtp.

smtp      inet  n       -       n       -       -       smtpd
  -o content_filter=spamassassin

Also add the following service entry for SpamAssassin

spamassassin unix -     n       n       -       -       pipe
  flags=R user=spamd argv=/usr/bin/vendor_perl/spamc -e /usr/bin/sendmail -oi -f ${sender} ${recipient}

Now you can start and enable spamassassin.service.

SpamAssassin combined with Dovecot LDA / Sieve (Mailfiltering)

Set up LDA and the Sieve-Plugin as described in Dovecot#Sieve. But ignore the last line mailbox_command... .

Instead add a pipe in /etc/postfix/master.cf:

 dovecot   unix  -       n       n       -       -       pipe
       flags=DRhu user=vmail:vmail argv=/usr/bin/vendor_perl/spamc -u spamd -e /usr/lib/dovecot/dovecot-lda -f ${sender} -d ${recipient}

And activate it in /etc/postfix/main.cf:

 virtual_transport = dovecot

SpamAssassin combined with Dovecot LMTP / Sieve

Set up the LMTP and Sieve as described in Dovecot#Sieve.

Edit /etc/dovecot/conf.d/90-plugins.conf and add:

 sieve_before = /etc/dovecot/sieve.before.d/
 sieve_extensions = +vnd.dovecot.filter
 sieve_plugins = sieve_extprograms
 sieve_filter_bin_dir = /etc/dovecot/sieve-filter
 sieve_filter_exec_timeout = 120s #this is often needed for the long running spamassassin scans, default is otherwise 10s

Create the directory and put spamassassin in as a binary that can be ran by dovecot:

 # mkdir /etc/dovecot/sieve-filter
 # ln -s /usr/bin/vendor_perl/spamc /etc/dovecot/sieve-filter/spamc

Create a new file, /etc/dovecot/sieve.before.d/spamassassin.sieve which contains:

 require [ "vnd.dovecot.filter" ];
 filter "spamc" [ "-d", "127.0.0.1", "--no-safe-fallback" ];

Compile the sieve rules spamassassin.svbin:

 # cd /etc/dovecot/sieve.before.d
 # sievec spamassassin.sieve

Finally, restart dovecot.service.

Rule-based mail processing

With policy services one can easily finetune Postfix' behaviour of mail delivery. postfwd and policyd^AUR provide services to do so. This allows you to e.g. implement time-aware grey- and blacklisting of senders and receivers as well as SPF policy checking.

Policy services are standalone services and connected to Postfix like this:

/etc/postfix/main.cf

smtpd_recipient_restrictions =
  ...
  check_policy_service unix:/run/policyd.sock
  check_policy_service inet:127.0.0.1:10040

Placing policy services at the end of the queue reduces load, as only legitimate mails are processed. Be sure to place it before the first permit statement to catch all incoming messages.

Sender Policy Framework

To use the Sender Policy Framework with Postfix, install python-postfix-policyd-spf^AUR.

Edit /etc/python-policyd-spf/policyd-spf.conf to your needs. An extensively commented version can be found at /etc/python-policyd-spf/policyd-spf.conf.commented. Pay some extra attention to the HELO check policy, as standard settings strictly reject HELO failures.

In the main.cf add a timeout for the policyd:

/etc/postfix/main.cf

policy-spf_time_limit = 3600s

Then add a transport

/etc/postfix/master.cf

policy-spf  unix  -       n       n       -       0       spawn
     user=nobody argv=/usr/bin/policyd-spf

Lastly you need to add the policyd to the smtpd_recipient_restrictions. To minimize load put it to the end of the restrictions but above any reject_rbl_client DNSBL line:

/etc/postfix/main.cf

smtpd_recipient_restrictions=
     ...
     permit_sasl_authenticated
     permit_mynetworks
     reject_unauth_destination
     check_policy_service unix:private/policy-spf

You can test your Setup with the following:

/etc/python-policyd-spf/policyd-spf.conf

defaultSeedOnly = 0

Sender Rewriting Scheme

To use the Sender Rewriting Scheme with Postfix, install postsrsd^AUR and adjust the settings:

/etc/postsrsd/postsrsd

SRS_DOMAIN=yourdomain.tld
SRS_EXCLUDE_DOMAINS=yourotherdomain.tld,yet.anotherdomain.tld
SRS_SEPARATOR==
SRS_SECRET=/etc/postsrsd/postsrsd.secret
SRS_FORWARD_PORT=10001
SRS_REVERSE_PORT=10002
RUN_AS=postsrsd
CHROOT=/usr/lib/postsrsd

Enable and start the daemon, making sure it runs after reboot as well. Then configure Postfix accordingly by tweaking the following lines:

/etc/postfix/main.cf

sender_canonical_maps = tcp:localhost:10001
sender_canonical_classes = envelope_sender
recipient_canonical_maps = tcp:localhost:10002
recipient_canonical_classes= envelope_recipient,header_recipient

Restart Postfix and start forwarding mail.

Troubleshooting

Warning: "database /etc/postfix/*.db is older than source file .."

If you get one or both warnings with journalctl

warning: database /etc/postfix/virtual.db is older than source file /etc/postfix/virtual
warning: database /etc/postfix/transport.db is older than source file /etc/postfix/transport

then you can fix it by using these commands depending on the messages you get

postmap /etc/postfix/transport
postmap /etc/postfix/virtual

and restart postfix.service

See also

• Official documentation
• Postfix Ubuntu documentation
• Out of Office for Squirrelmail