sometimes a reboot will do wonders. have you tried just turning your phone off and then on again? That is usually the first thing I do when i have a problem and more times than not it fixes the problem.
I was able to use yahoo mail via imap for about 2 weeks, then it just stopped no matter what I did. I think they block your account once they cast some kind of a "net" on those users who circumvent their paid service.
My account stopped syncing, saying login failed. Reboot doesn't help, tries to delete and re-add account, unable to validate my info. Confirmed username and password are correct, everything. Tried the K-9 app, says only tmo users can get free yahoo email.
Hey guys, just wanted to let you know that this happened to me also initially a few days ago and then all of a sudden, yesterday it started working again. I didn't do anything differently. Also, by the way, I'm using the "free" account.
Since Yahoo does not formally support IMAP, and support POP3 only for paid accounts, I'd think that it would probably work unreliably more as the norm.