Another possible scenario is that Gmail is getting wires crossed. I have had the account [email protected] for 20 years now. About 5 years ago, some dude in Australia (who coincidentally has the same rare last name as me) started using [email protected]. Based on the emails I've seen I believe that Gmail let him do this for a while, but eventually started delivering his emails into my inbox. I don't know if there was a technical change in Gmail for how they handled these addresses or what, but it's very odd.