Some servers have us marked as so spam we don't even show up in the spam folder (hotmail does this)
Actually, as of a couple of months ago, Hotmail doesn't. But for some reason the provider I've used for many years (mail.com) now doesn't let it through. And pretty much every other provider I've had , not including Google, blocks it.
There is something about the format or sending server that makes playdip messages look terribly like spam to filter providers. Too bad, and it should be a solvable problem, but until then sticking with a Google is the safest option, I guess.