I can't figure out what's misconfigured. I can send and receive email fine. I've added a line to /etc/aliases: baz: firstname.lastname@example.org Where user exists and has been confirmed to receive mail. When I send to email@example.com, postfix expands the alias but then bounces back to sender saying firstname.lastname@example.org is unknown. If I just click the "unknown" address in the bounce message, Mail creates a message to that sender, and it delivers without an issue. I've been pulling my hair out over this for days. Eventually baz should have multiple destinations, but I can't even get this simple case to fire. Any ideas what I'm doing wrong?