I haven't been able to solve this issue that recently popped up for me. Around the same time that I updated Outlook 2011 for Mac to 14.4.5 I also changed servers that I receive email from.

When I delete an email from any IMAP account (5 different email accounts all on the same server but different domains) I shortly thereafter get a "Message Unavailable" from "System Administrator." Sometimes, but not all the time, this Message Unavailable will go away with the next refresh, but most of the time it stays there.

Outlook is set to download the entire IMAP message, not just the header. There are no other active clients receiving email, however when I do receive/view/send/delete from another client, such as my iPhone I do not have any issue like this. I've done the obligatory rebuild of the database.

Can anyone help me out on this issue?