Hello Community:
We recently migrated all users (150) to Exchange 2016 from 2013. We have retired all 2013 servers and are a single-server Exchange 2016 environment. We have enabled MAPI over HTTP on the organization and on the MapiVirtualDirectory we have set both internal and external URLs along with the IISauthenticationMethods to NTLM, Negotiate. Based on what I can tell, this is working correctly. Autodiscover works fine, Outlook anywere works with no issues. New domain joined and external Outlook clients find the server and connect with no issues. Connection status shows protocol HTTP and Encrypt SSL. However, we are having various performance issues with mailboxes and on a number of occasions we are getting a popup message stating : "Changes made to the item were lost because of a reconnect with the server." I have ensured these users have new Outlook profiles and have in a few cases upgraded to Outlook 2016 from Outlook 2013 to no avail. No strange server event log errors. If I disable MAPI over HTTP and go back to using RPC/HTTP things seem to be fine.
Thoughts on what could be causing this?
JC