We have deleted all Outlook profiles from the MS User Data folder multiple times and let it rebuild from the server.  We have removed all Outlook data and preferences, we have uninstalled an reinstalled MS Office, we have completely rebuilt the Mac from the ground up (new OS, new Office suite), and still these error occur several times a day.  Sometimes mail will send right away, other times it takes multiple attempts (as many is 15-20) before a message will send.  Sometimes messages will seem to send, but instead will appear unsent in the Drafts folder days or even weeks later.

On the receiving end, there are times when her Mac Outlook will be 5-6 hours behind on mail, while her iPhone is getting everything right away.  If she logs into an Windows machine, her mail works fine.  Sometimes her mail will stall for days and she is forced to revert to using OWA for communication. She has a large volume of mail, over 15,000 in the inbox alone.  Filed mail counts over 100,000 messages, which is slightly below average in our organization.  No other Mac user is having these issues.

She also regularly receives the error, "Microsoft Outlook must be closed because an error occurred.  Any unsaved work may be lost."

Could there be something wrong with her Exchange mail account or profile?  It seems we have eliminated everything on the workstation side.

Thanks for any help you can provide.