Receiving emails from my own spoofed domain

Hi, This might be a stupid question, but I recently received a email spam from one of my users u...@mydomain.com, which was spam. After asking her about it and afterwards checking logs, it turns out it came from some random Brazilian server (and she was not hacked *sigh of relief*). But the spam e

Forward emails recieveing error: Recipient address rejected: User unknown in local recipient table

Hi, I have one domain - example.com. And I'd like to have user mailboxes on two separate machines (policy differences), but ran into a problem with sending emails from a user on one machine to users on the other machine. The error message : 550 5.1.1 : Recipient address rejected: User unknown in l