Had it happen to me many years ago when all my domains werent consolidated at one registrar.. Let one of my email address domains expire which i didnt know was on the whois for another domain ( the only one i hadnt updated )
This probably happens more often than you can imagine.
The dumbest thing is that i get people putting something @ mydomains as their email address when they signup for stuff hundreds of times a day.. so i actually get their account info emailed directly to me. I never do anything with it, but i can imagine what others would do.