Whilst working in corporate I tried to get matt@apple.com which was showing as free, but in fact somebody in retail had claimed it. Good for them!
that didn't stop me from registering it again at my next employer, where i received more complaints, but in this case they were less out there and i actually knew the people who could do something about them (smaller company, support shadowing shifts), and there i was eventually able to wire the alias into their official process after forwarding enough of them to the people i knew.