Date: 2006may16 Updated: 2007feb23 Updated: 2010jan21 Product: Postfix Q. Postfix: I prevent (well, slow down) backscatter from Postfix A. Backscatter is when spammers use your server to send spam via bounces. The solutions is to REJECT and not BOUNCE unrecipient mails. - If you are using Postfix 1.x, upgrade to Postfix 2.x - Use these Postfix options:

unknown_local_recipient_reject_code = 550 smtpd_error_sleep_time = 0

They'll reject (not bounce) unknown recips - If you are using Mailman, make sure you have:

autorespond_postings=no

For all lists. ------------------------------------------------------ In postfix 1.x you might be tempted to do:

root "| exit 67"

in the /etc/postfix/aliases file. This generates a user unknown message. But in, Postfix 1.x, its sent as a bounce. A spammer sender might have intended this and forged a return address. This is called backscatter. A solution I found is to weed out these addresses in the /etc/postfix/regexp_table file.