We are using Outlook for Mac 2011, ver 14.4.1, tied to outlook.office365.com.

We have several Mac users accessing three shared mailboxes, and have for several months. Starting April 9, 2014, we were unable to send from the shared mailboxes directly, instead getting "HTTP error. The server cannot fulfill the request.", and the email is moved to the user's Drafts folder. If the user opens the draft and attempts to resend the email from their personal account, the email goes through.

Attachment/no attachment does not make a difference. Deleting the user profile and recreating has not made a difference, aside from creating a 'hang' situation where the shared email does not release into drafts. (Tried 3 times).  Rebuilding the Microsoft Database Utility did not make a difference.

Accessing the shared mailbox via outlook.office365.com does allow us to send from the shared accounts. PC users are able to send from the shared accounts. The Mac users are able to read, delete, move emails between shared boxes and into their personal boxes.  Only functionality lost is sending email out.

In looking through the Applications/Microsoft Office 2011 folder there appears to be a large number of files that were updated on April 9th. The 14.4.1 update has been applied to all the machines, as it was marked as Critical. I don't see this specific issue listed in the Known issues in Outlook 2011 page, but it's not been updated since Sept 2013 either.

Any suggestions are appreciated, my corporate IT staff has not had any luck.