Saturday, 14. April 2018 Week 15
Wednesday, 4. April 2018 Week 14

Exclude domain from unknown sender check

Postfix provides the reject_unknown_sender_domain check which allows to only accept incoming e-mails sent from domains which actually exist.

Unfortunately there exists this one external service which uses a non-existing subdomain to send their notification e-mails. Thus all their notifications get rejected.

The following configuration allows to keep the reject_unknown_sender_domain check in place, but to exclude a specific domain from this check.

# snippet in main.cf
smtpd_sender_restrictions = check_sender_access pcre:/etc/postfix/sender_domain_verification
# exclude regex in sender_domain_verification
!/@domain\.to\.exclude\.com$/ reject_unknown_sender_domain

Your distribution might ship Postfix support for pcre matches in a dedicated package which needs to be installed separately (in the case of Debian you need to install the postfix-pcre package).

Sunday, 1. April 2018 Week 13