IMAP authentication failure even though mail works

even though the two accounts on the left column work without an issue, every time I launch eM, it asked me for an IMAP username/password. Even though I bypass it, my mail continues to flow without issue. It seems that there is a half provisioned account.

Hi, please try to delete and add your account again. If it will continue and you are still able to receive and send your emails then write me back again.

Also what email service provider do you use? This is quite usual behaviour for Yahoo.