Anecdotally, almost every email I see in my gmail inbox is advertisement of some sort. There's newsletters I never signed up for, special offers from companies I've never had dealings with, it never ends.

Some of it hasn't even been sent to me as an email, but shows up in the inbox as though it was an email.

Granted, there's fewer scam emails than in my non-gmail inbox, but man is there a lot of spam.