Postfix relay_domains problem VS Spam
I've got a configuration issue with Postfix. Hope you can help me.
We have many websites on the Internet (say mycompanie.com, a.com, b.com, c.com and d.com). We also have different emails with those domains, so users can contact the admin on each of them (say firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com and firstname.lastname@example.org).
Postfix is configured to accept mail from any domain listed in the "relay_domains" parameter. So, mycompanie.com, a.com, b.com, c.com and d.com are in. When i try to send an email to email@example.com, it goes through (and it's perfect). When i try firstname.lastname@example.org, it doesn't take it (and it's still perfect, since admin123 is not a local user and is not in the alias table). When i try email@example.com, it goes through (and it's ok, since firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, are aliases to, say, firstname.lastname@example.org).
BUT when i try email@example.com, or firstname.lastname@example.org it also accept it. email@example.com is not a local user, nor an alias... So the email comes in, Postfix processes it, and bounce it back to the sender... Usually, it is spam, so it would be much better to stop it right on the front door.
THE QUESTION: How can i always check if the destination user exists, and if not, break the connection?
Here is my "local_recipient_maps" parameter
local_recipient_maps = proxy:unix:passwd.byname $alias_maps