YAM 2.9p1 stopped working with my mail provider for no apparent reason, and from this thread it looks like it's stopped working with a lot of mail providers. In my case, my provider changed something on the server end and YAM doesn't like it.
The YAM nightly build worked for me, but those have expiration dates and I haven't tried to keep up to date. I'm hopeful that the next formal release will have this issue fixed.