Sometimes it is just a question of definitions. If I get an email from my mum with an ebook attached, I can regard it as a task (to add that ebook to my reader, to write back later). I'd argue that this is not the definition of a task, the writing back part alone especially not. That is just communication.

But sure, if you use emails primarily to collaborate with others, for you the emails are task thinking might very well be true.