That may be
But it can be just his way of using the word as well. People tend to use it in whatever ways possible
Still it's obvious - just ask him how he calls all the messages he receives, when he has to tell, e.g. how many he receives say per day or per month
I mean he has to say smth. like "I've received ten emailS", doesn't he? It is to prove that the context is of the primary importance in such cases, and this noun can be both - countable and uncountable.