I would like to setup a mail bouncer for a group of people. A sort of simple mailing list. The server is running postfix.
When people email email@example.com, their mail is sent to a number of people on a list who’s members are outside of the example.com (that config is outside of this question and is already working for single forwarding addresses)
Senders are unauthenciated and from any domain. e.g. firstname.lastname@example.org Their address is already stored locally in a membership database.
However that would allow a spammer (should they discover the ‘group’ address) to use the server as a trampoline for spam. email@example.com is not in the database.
So I want to restrict the access to a limited list using sender_access and a backend database.
But I don’t want to block the server as a normal SMTP final destination for all other email.
I.e. mail from firstname.lastname@example.org to email@example.com is processed normally
I know I can use sender_access (or check_sender_access) and a backend database to check the MAIL_FROM. But that would apply to all email.
I only want sender_access to apply to mail intended for firstname.lastname@example.org so that email@example.com is blocked as their address is not in the database.