LINUX SYSLOGD PERFORMANCE
=========================

LINUX syslogd uses synchronous writes by default, which is very
expensive. For services such a mail it is recommended that you
disable synchronous logfile writes by prepending a - to the logfile
name:

    mail.*                          -/var/log/mail.log

SPAM BLOCKING SOURCE ROUTED ADDRESSES
=====================================

If you relay mail for other domains, you must prevent unauthorized
relay of addresses such as:

    user@elsewhere@the.other.domain
    user%elsewhere@the.other.domain
    elsewhere!user@the.other.domain

The simplest solution is to install a regular expression filter:

    /etc/postfix/main.cf: 
	smtpd_recipient_restrictions = regexp:/etc/postfix/regexp_access

    /etc/postfix/regexp_access:
	/[%!@].*@/ 550 Sender specified routing is not supported here.

For the local domain, Postfix will do the right thing with:

    user@elsewhere@my.own.domain
    user%elsewhere@my.own.domain
    elsewhere!user@my.own.domain

That is, it bounces the first form because "user@elsewhere" is not
a valid local user, and it accepts the second and third forms only
when user@elsewhere is a valid relay destination.

