It is relatively safe to turn on sender address verification for specific domains that often appear in forged email.
/etc/postfix/ main.cf: smtpd_sender_restrictions = hash:/etc/postfix/sender_access unverified_sender_reject_code = 550 # Note 1: Be sure to read the " Caching" section below! # Note 2: Avoid hash files here. Use btree instead. address_verify_map = btree:/var/mta/verify /etc/postfix/sender_access: aol.com reject_unverified_sender hotmail.com reject_unverified_sender bigfoot.com reject_unverified_sender ... etcetera ...
At some point in cyberspace/time, a list of frequently forged MAIL FROM domains could be found at https://www.monkeys.com/anti-spam/filtering/sender-domain-validate.in.
NOTE: One of the first things you might want to do is to turn on sender address verification for all your own domains.
