Turn on reject_sender_login_mismatch

[andersk]

To help cut down on outgoing spam, we should require that mail sent directly through Scripts carry a matching @scripts.mit.edu address or an address at a matching Scripts vhost. After all, if you want to send mail from @mit.edu, @gmail.com, etc., you should be sending it through outgoing.mit.edu, smtp.gmail.com, etc.—a mismatch here would be an SPF violation anyway.

I think this would be achieved by ​smtpd_sender_restrictions = reject_sender_login_mismatch, with ​$smtpd_sender_login_maps configured in correspondence with our $virtual_alias_maps.

This probably implies disabling SMTP to localhost:25.

[quentin]

SMTP to localhost should be fine - we can still authenticate the socket.

[andersk]

Does Postfix implement that kind of authentication?

Separately, we may need another check to match the MAIL FROM address with the From: or Sender: header.

[quentin]

It's been a while since I looked into it, but IIRC my conclusion was that Postfix doesn't natively implement it, but you could write an authentication plugin for smtpd_sender_restrictions that checks it.