The Administrative logging is a great resource for finding email clients that may be problematic or misconfigured. Administrators should periodically review this log to find clients of concern. Ensuring that clients are connected properly will improve the overall health of your server, as it prevents these clients from spamming the server with invalid calls.
NOTE: The Administrative logging can currently provide information on Outlook MAPI clients that are misconfigured. However, in the future, it will be a hub for finding misconfigured connections from all Exchange protocols, including EWS and EAS.
If an Outlook MAPI client is misconfigured, here's an example of the log you'll find in the Administrative logs:
[2021.12.21] 00:02:00.319 MAPI Guid mismatch (source) email caller [USER@DOMAIN.TLD] email owner [USER@DOMAIN.TLD] server [00000000-0000-0000-0000-000000000000] source [guid 00000000-0000-0000-0000-000000000000 global counter 217852529]
To resolve this issue you should: