I run a Postfix + Dovecot email server for my personal email. Common setups include
reject_unknown_reverse_client_hostname for SMTP clients to reduce invalid connections attempts, but this became a problem when my new metro wireless ISP assigned me an IP that has no PTR record, causing my mail server to reject my own local email client’s SMTP connections!
In this post I present two solutions: simply adding
permit_sasl_authenticated to the SMTP client restrictions, or implementing a more complex but generic whitelist via
check_client_access and a MariaDB (or MySQL) database table.