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Browse - Computer Tips - How can I prevent (well, slow down) backscatter from Postfix?

Date: 2006may16
Updated: 2007feb23
Updated: 2010jan21
Product: Postfix

Q.  How can 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:
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.

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