Introduction

In this howto, Postfix integration with amavis-new will be presented. Amavis-new is a wrapper that can call any number of content filtering programs for spam detection, antivirus, etc. In this howto, integration with Spamassassin and Clamav will be presented. This is a classical installation of Postfix + Amavis-new + Spamassassin + Clamav.

Prerequisite

You should have a functional Postfix server installed. If this is not the case, follow the Postfix guide.

Installation

To begin, install (see InstallingSoftware) the following packages: 

sudo apt-get install amavisd-new spamassassin clamav-daemon

Install the optional packages for better spam detection (who does not want better spam detection?): 

sudo apt-get install libnet-dns-perl libmail-spf-perl pyzor razor

Install these optional packages to enable better scanning of attached archive files: 

sudo apt-get install arj bzip2 cabextract cpio file gzip lha nomarch pax rar unrar unzip unzoo zip zoo

Note: Ubuntu 12.04 LTS doesn't have unzoo. Ubuntu 14.04 LTS doesn't have lha. You may try to substitute lhasa.

Configuration

Clamav

The default behaviour of Clamav will fit our needs. A daemon is launched (clamd) and signatures are fetched every day. For more Clamav configuration options, check the configuration files in /etc/clamav.

Add clamav user to the amavis group and vice versa in order for Clamav to have access to scan files: 

sudo adduser clamav amavis
sudo adduser amavis clamav

Note: especially when driven on small cloud instances, VPS or routers there were concerns about the memory consumption. There is a good summary why virus scanning in general has a rather high memory consumption in general. An admin setting up such a solution needs to consider that ~200-350mb seem to be rather normal.

Spamassassin

As amavis is its own spamassassin-daemon (amavis uses the spamassassin libraries), there is no need in configuring or starting spamassassin. amavis will not use any running instance of spamd!

The use of razor and pyzormust be enabled by 

# su - amavis -s /bin/bash
# razor-admin -create
# razor-admin -register
# pyzor discover

There is no need of configuring razor or pyzor.

Amavis

First, activate spam and antivirus detection in Amavis by editing /etc/amavis/conf.d/15-content_filter_mode: 

use strict;

# You can modify this file to re-enable SPAM checking through spamassassin
# and to re-enable antivirus checking.

#
# Default antivirus checking mode
# Uncomment the two lines below to enable it
#

@bypass_virus_checks_maps = (
   \%bypass_virus_checks, \@bypass_virus_checks_acl, \$bypass_virus_checks_re);


#
# Default SPAM checking mode
# Uncomment the two lines below to enable it
#

@bypass_spam_checks_maps = (
   \%bypass_spam_checks, \@bypass_spam_checks_acl, \$bypass_spam_checks_re);

1;  # insure a defined return

After configuration Amavis needs to be restarted: 

sudo /etc/init.d/amavis restart

Postfix integration

For postfix integration, you need to add the content_filter configuration variable to the Postfix configuration file /etc/postfix/main.cf. This instructs postfix to pass messages to amavis at a given IP address and port: 

content_filter = smtp-amavis:[127.0.0.1]:10024

The following postconf command, run as root because of the preceding sudo command, adds the content_filter specification line above to main.cf: 

sudo postconf -e "content_filter = smtp-amavis:[127.0.0.1]:10024"

Alternatively, you can manually edit main.cf yourself to add the content_filter line.

Next edit /etc/postfix/master.cf and add the following to the end of the file: 

smtp-amavis     unix    -       -       -       -       2       smtp
        -o smtp_data_done_timeout=1200
        -o smtp_send_xforward_command=yes
        -o disable_dns_lookups=yes
        -o max_use=20

127.0.0.1:10025 inet    n       -       -       -       -       smtpd
        -o content_filter=
        -o local_recipient_maps=
        -o relay_recipient_maps=
        -o smtpd_restriction_classes=
        -o smtpd_delay_reject=no
        -o smtpd_client_restrictions=permit_mynetworks,reject
        -o smtpd_helo_restrictions=
        -o smtpd_sender_restrictions=
        -o smtpd_recipient_restrictions=permit_mynetworks,reject
        -o smtpd_data_restrictions=reject_unauth_pipelining
        -o smtpd_end_of_data_restrictions=
        -o mynetworks=127.0.0.0/8
        -o smtpd_error_sleep_time=0
        -o smtpd_soft_error_limit=1001
        -o smtpd_hard_error_limit=1000
        -o smtpd_client_connection_count_limit=0
        -o smtpd_client_connection_rate_limit=0
        -o receive_override_options=no_header_body_checks,no_unknown_recipient_checks

Also add the following two lines immediately below the "pickup" transport service: 

         -o content_filter=
         -o receive_override_options=no_header_body_checks

This will prevent messages that are generated to report on spam from being classified as spam.

For Postfix instances hosting virtual domains, Amavis also need to know what domain names are considered as local domain names. By default, only the FQDN of the localhost is treated as local. So in the file '/etc/amavis/conf.d/05-domain_id', list all your virtual domain names in @local_domains_acl 

         @local_domains_acl = ( ".$mydomain", ".example1.com", ".example2.com" );

And In the file '/etc/amavis/conf.d/50-user', add 

         @whitelist_sender_acl = @local_domains_acl

More information can be found from "README.postfix from amavisd-new" and "D.J.Fan"

Reload postfix: 

sudo /etc/init.d/postfix reload

Now content filtering with spam and virus detection is enabled.

Test

First, test that the amavis SMTP is listening: 

telnet localhost 10024
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 [127.0.0.1] ESMTP amavisd-new service ready
^]

Check on your /var/log/mail.log that everything goes well. If you raise the log level, you can check every step of the content filtering: spam check, virus check, etc. Don't forget to lower the log level after your checks!

On messages that go through the content filter you should see: 

X-Spam-Level: 
X-Virus-Scanned: Debian amavisd-new at example.com
X-Spam-Status: No, hits=-2.3 tagged_above=-1000.0 required=5.0 tests=AWL, BAYES_00
X-Spam-Level:

Note: $sa_tag_level in /etc/amavis/conf.d/20-debian_defaults must be lower than spam hit rating for the header to appear on the message. For troubleshooting set $sa_tag_level to -999

Troubleshooting

If the filtering is not happening, adding the following to /etc/amavis/conf.d/50-user may help: 

@local_domains_acl = ( ".$mydomain" );

If you receive mail for other domains, add them to the list. This information was obtained from the Amavis-New FAQ here.

If you see the following error in /var/log/syslog when amavisd is trying to scan a message:

amavis[30807]: (30807-01) (!!) ask_av (ClamAV-clamd) FAILED - unexpected result: /var/lib/amavis/tmp/amavis-20070615T125025-30807/parts: lstat() failed. ERROR\n

Try changing the permissions on /var/lib/amavis/tmp: 

chmod -R 775 /var/lib/amavis/tmp

You can also change AllowSupplementaryGroups in /etc/clamav/clamd.conf: 

AllowSupplementaryGroups true

Another way to trouble shoot errors associated with Amavisd-new, Spamassassin, Postfix, or Clamav is to restart all the services with Amavisd-new being the last one to start: 

sudo /etc/init.d/postfix restart
sudo /etc/init.d/spamassassin restart
sudo /etc/init.d/clamav-daemon restart
sudo /etc/init.d/amavis restart

Then check /var/log/mail.log and see if the error has gone away.

Note: $sa_tag_level in /etc/amavis/conf.d/20-debian_defaults must be lower than spam hit rating for the header to appear on the message. For troubleshooting set $sa_tag_level to -999

Amavis Performance

To increase the number of processes that amavisd-new uses above the default 2 edit the file /etc/amavis/conf.d/50-user inserting the line: 

$max_servers = X;

above the line: 

#------------ Do not modify anything below this line -------------

where X is the number of processes you wish amavis to use.

Amend the following line in /etc/postfix/master.cf with the same value for the max_procs (marked below as X) 

smtp-amavis     unix    -       -       -       -       X       smtp

Restart amavis and reload postfix's config 

sudo /etc/init.d/amavis restart
sudo postfix reload

You can check the configuration change has taken affect by running amavisd-nanny: 

sudo amavisd-nanny

For guidance on how many processes to set this value to please see: 

zcat /usr/share/doc/amavisd-new/README.performance.gz | less

and http://www.ijs.si/software/amavisd/amavisd-new-magdeburg-20050519.pdf


Note: This guide has been tested on Ubuntu 7.10 (Gutsy Gibbon), Ubuntu 10.04 LTS Server (Lucid Lynx), Ubuntu 12.04.3 LTS (Precise Pangolin), Ubuntu 14.04.2 LTS (Trusty Tahr), and Ubuntu 20.04 LTS (Focal Fossa).

PostfixAmavisNew (last edited 2022-02-14 00:03:52 by kylechine-leismore)