Here is the description how to install AntiVir MailGate to work with postfix:

First you have installed AntiVir MailGate described in INSTALL.

There are two possible ways of integrating AntiVir MailGate under
postfix. One of these is to make AntiVir MailGate listen at port 25
and forward the emails to postfix. The other is to integrate AntiVir
MailGate in postfix as content filter. This is possible from 
the Snapshot 20000520 version of postfix onwards. A release with
content filtering capacity is available from version 20010228 onwards.
We prefer to use the content filter method because the whole SMTP functionality
of Postfix will be available.

1. Content filter 
-----------------

   Edit the /etc/services and add the following entries:
    # Content Filter for postfix
    antivir 10024/tcp #Port for avgated
    smtp-backdoor 10025/tcp #Port for postfix backdoor

   Edit /etc/avmailgate.conf and modify the following entries:

    # Select interface and port, the smtp daemon will listen on.
    # Port may be given as a number or a service name.
    ListenAddress localhost port antivir

    # Select how mail should be forwarded.
    # Send mail by piping it thru sendmail (this is the default)
    #ForwardTo /usr/sbin/sendmail -oem -oi
    # Or if you want the mail to be sent by SMTP
    ForwardTo SMTP: localhost port smtp-backdoor

   If you are using SuSE Mail Server 2 change also the following
   line from:
    #AllowSourceRouting NO
   to:
    AllowSourceRouting YES

   Close AntiVir MailGate and restart it: /etc/init.d/avgate restart
   Insert the following entry in /etc/postfix/master.cf:

    # service type private unpriv chroot wakeup maxproc command + args
    # (yes) (yes) (yes) (never) (50)
    smtp     inet   n        -      n       -      -     smtpd
    # Für AntiVir Maildämon
    localhost:smtp-backdoor inet n - n - - smtpd -o content_filter=

   Make sure that the first character in the table is not a space.
   The entry smtpd -o content_filter deactivates the relevant line in a
   second invocation of postfix. (to avoid generating a mail loop!)

   Insert the following entry in /etc/postfix/main.cf:

    # Antivir Einbindung
    content_filter = smtp:127.0.0.1:10024

   Restart postfix:
    /etc/init.d/postfix restart

   Note:
   If postfix sets all emails to status "deferred" after installing
   AntiVir MailGate search the line:
    defer_transports = local

   and add the following comment char using #:
    #defer_transports = local


2. Listening on port 25  
-----------------------

   This is the second way how to implement AntiVir MailGate in postfix:

   Edit the file master.cf. Locate the following line:
    smtp inet n - n - - smtpd

   and add the following comment char using #:
    #smtp inet n - n - - smtpd

   This will prevent postfix from listening at the SMTP port, and enable
   avgated to do so instead. Emails forwarded by avgatefwd will then be
   processed by sendmail wrapper /usr/lib/sendmail, which is included
   with postfix.

   Restart postfix: 
    /etc/rc.d/postfix restart