efa-project.org

Is it possible to get an email sent back to users when an email they send out is blocked for any reason i.e bad content / spam etc?

Why not just whitelist your internal server?

Can I ask this question again. In particular if I tick SMTP Client Restrictions > Reject clients with no reverse hostname

I didn't see the relevance to whitelisting your internal server.

Thanks

If you enable that option, postfix will reject smtp client connections that don't have a valid reverse mapping. See here for an explanation

postfix will return a temporary error code of 450 (default settings) that tells the smtp client to retry later. If the smtp client is a valid smtp server, it should keep retrying until either it successfully delivers the message, or it gives up. If it gives up (sometimes after a couple of days), it should send a message to the sender, therefore there is nothing you need to do.

I suppose you could change the error to a 5xx series error which should notify the sender faster.

(someone please correct me if my understanding is incorrect)