Consider yourself lucky. When I get such reports, I very rarely get something as useful as an email address to key off.
> "I'm not getting emails from Jim at Acme Corp any more"
< "OK, is that jim@, james@, jim.smith@, james.smith@, jsmith@, ..."
> "I don't know. I think he uses gmail"
< "Ah, alright, I know how to fix this. Let me just find my cattle prod"