Date: 2006May16, 2007Feb23
Subject: backscatter
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.
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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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