I have Postfix SMTP configured to require authentication for relaying mail to outside world.
When an outside SMTP server want to deliver mail to my domain (destination: firstname.lastname@example.org), authentication is not necessary - this is the way things worked for me - to be able to receive email from outside world and still avoid open relay. But I would be delightful if I could configure Postfix to require authentication for clients which presents themselves as local users, regardless of their destination mail address, preferably without header checks as they have tremendous performance impact.
Why would I need this? Because an imposter could deliver mail to my local users and represent himself as another local user. Eve just sent an email from email@example.com to firstname.lastname@example.org, unauthenticated, using this SMTP server. And Alice and Bob are in fight.
I need auth required for elho email@example.com