Postfix (简体中文)
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
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
~/.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 = $myhostname, localhost mynetworks_style = host default_transport = error: outside mail is not deliverable
所有其他设置维持不变。 完成上面这个配置后，你可能还想配置一些#别名 Aliases参数，然后#启动 Postfix。
虚拟用户邮件(Virtual mail)
虚拟用户邮件的邮件账户不存储在本地系统的(/etc/passwd文件中。可以配合数据库完成对用户账户的存储。
请参见 Virtual user mail system with Postfix, Dovecot and Roundcube (简体中文) 那是一个如何设置的详细介绍。
检查配置 Check configuration
运行postfix check 命令来完成配置检查。它会输出所有你在配置文件中可能写错的东西。
运行postconf命令可以查看所有的配置。运行postconf -n命令可以查看与默认配置的区别。
启动 Postfix
newaliases命令才能让 Postfix 正常运行。启动 postfix.service 服务。
TLS
You need to obtain a certificate.
For more information, see Postfix TLS Support.
Secure SMTP (sending)
By default, Postfix/sendmail will not send email encrypted to other SMTP servers. To use TLS when available, add the following line to main.cf:
/etc/postfix/main.cf
smtp_tls_security_level = may
要强制使用TLS (这种情况下如果远程服务器不支持的话会导致失败), 只需要把 may 变更为 encrypt 就行了。 值得注意的是，如果此邮件服务是一个公开的服务(相对于企业内部服务，不对公网提供服务的那种)时，这样的做法会违反 RFC:2487 ，所以请慎重考虑。
Secure SMTP (receiving)
By default, Postfix will not accept secure mail.
To enable STARTTLS over SMTP (port 587, the proper way of securing SMTP), add the following lines to main.cf
/etc/postfix/main.cf
smtpd_tls_security_level = may smtpd_tls_cert_file = /path/to/cert.pem smtpd_tls_key_file = /path/to/key.pem
In master.cf, find and uncomment the following lines to enable the service on that port with the correct settings:
/etc/postfix/master.cf
submission inet n - n - - smtpd -o syslog_name=postfix/submission -o smtpd_tls_security_level=encrypt -o smtpd_sasl_auth_enable=yes -o smtpd_tls_auth_only=yes -o smtpd_reject_unlisted_recipient=no # -o smtpd_client_restrictions=$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:
[email protected] 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
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
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.
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
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 policydAUR 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-spfAUR.
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 postsrsdAUR 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