Reject mails in postfix based on sender domain

Some bash lines to generate sender checks for postfix.

NOTE: it turned out that this can get dangerous; for example, if you mark a mail coming from gmail.com spam, you’ll reject gmail.com, which is obviously not a bright idea. I’ll leave the article here, but be warned.

Recently I noticed that I get many spams from the same sender domains. In this case, I could safely apply a manually updated list to postfix to reject these domains in the first place.

Go to the spam Maildir’s cur folder:

#!/bin/bash

cd /path/to/spam/Maildir/cur

touch /etc/postfix/sender_checks
grep -ri ^From * | awk '{ print $3}' | grep @ | sed 's/[<>]//g' | cut -d"@" -f2 | sort | uniq >/tmp/spammer
sed -i "s/^/\//g" /tmp/spammer
sed -i "s/$/\$\/ REJECT\ Byez\ spammer/g" /tmp/spammer
cat /etc/postfix/sender_checks >> /tmp/spammer
cat /tmp/spammer | sort | uniq > /etc/postfix/sender_checks

Add to /etc/postfix/main.cf:

smtpd_sender_restrictions = reject_unknown_sender_domain,
    check_sender_mx_access pcre:/etc/postfix/sender_checks,
    check_sender_access pcre:/etc/postfix/sender_checks,
    check_sender_ns_access pcre:/etc/postfix/sender_checks,

It will not catch too many spams only a few per day, but even that can be useful.



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