Hi there, just thought I would let you know that I have had this problem a few times and chatting with apple support solved this problem. Simply remove account and reset account under other accounts. Problem solved, this works every time yet have not seen this solution on sites before. Hope this helps everyone!!
Thanks for the useful tip , in case if IMAP account has some issues , take back up of all mails ( ~/Library - mail - V3 folder for EL- CAPITAN users and V2 for yosemite users ) , delete the corrupted IMAP account and once again form a new one .
thanks for that info, just surprised I couldn't find the simple solution I posted. Guys in support offered this solution almost a year ago, and I forgot about it until it happened again, and yet again they told me what to do.
email account wont go online
