"Mail was unable to open this mailbox on the server "p66-imap.mail.me.com"

For months I've been having weird random issues with my mail. I can no longer use Outlook for both of my mail accounts, have to use the Apple/Mac mail program for one of them. A few weeks ago even though I haven't changed anything on the local system I began getting errors about missing mailboxes. In this case it says it can move messages to "Bulk Mail", followed by the subject, then "The server returned the error: Mailbox does not exist (took 3 ms)."

Do I need some holy water? Or should I just stop using Apple mail and go with Outlook?