Joe Jobbing countermeasures

This is effective agains joe jobs.

1) Turn on local_recipient_maps to reject mail for non-existent users
(and relay_recipient_maps, if appropriate)

2) Set smtpd_error_sleep_time=0 in main.cf.

3) Set smtpd_timeout=10s in main.cf.

4) Add a header_checks regexp that triggers on bogus HELO hostnames
in the Received: headers of bounced mail:

/^Received:[[:space:]]*from[[:space:]]*porcupine.org/ reject forged helo

or whatever your domain name is. This relies on the fact that
spam/virusware sends the sender address's domain in the SMTP
HELO/EHLO command. All my systems send "EHLO hostname.porcupine.org"
so this pattern exposes forged mail.

Other sites might want to look at the IP address that is logged
along with the HELO hostname in the Received: header. If it's
not theirs, reject it.

Wietse