Hello,
Our users get this pop up a lot of times during the days. 
I set to track all email messages in Outlook. I tried some methods but the error wont go away. These are something I tried :
1. Change the synchronization time (30 minutes, 45 minutes, even 180 or 360 minutes)
2. Activate user mailbox and set server side synchronization
3. Turn on / off auto send, track in background
My goal is track everything in outlook & fix this error. I appreciate all your comments.
Thank you very much,