Its not technically mail (is an internal message system) and you don't hold that strict standard for anything else do you?, e.g. all tv commercials are spam because they show unsolicited commercial information, all billboard are spam...
Actually, yes in my viewpoint pretty much every billboard is spam. I've yet to see a billboard that informed me of something useful to me personally. (Let alone at an appropriate time! Is me driving on a highway an appropriate time to let me know that I should buy something? Hell no.)
