I don't think they have to be popular. My domain, which is more or less unadvertised, gets 2K+ spams per day. Nearly all are for accounts that don't exist.
Now, as some bogus accounts get lots of spam I think some people have signed up for crap using bogus emails at my domain, but that doesn't account for nearly all of it.
Also funny is that 1-2% of the spam isn't in English; most of that is Chinese/Japanese with the occasional ones that look like Cyrillic.
Outlook's junk mail filter catches about 97-98% of it; the rest is an easy cleanup.