Sometimes the event logs on Exchange servers throw up errors or warnings that do not appear again. The event ID, 4002 for MSExchange Availability is a broad error/warning/informational alert.

Looking a the error below, a Proxy request failed with an HTTP status code of 404 yet no users reported any errors, and no other issues were reported such as EWS not working and migrated users also had no issue.

The only thing that was going on was mailbox moves to Office 365 and the SSL certificate was only valid for another 3 days. The SSL certificate was renewed and the moves continued to completion but the error never presented itself again. Could this be a case of slowness with the migrations that generates these errors?

There may be some instances where the following is not set correctly but each environment is differently setup or managed:

A) Permissions on the virtual directories not configured or are configured
B) URL’s for EWS not configured or configured with the incorrect name
C) Autodiscover tests either showing the correct or incorrect URL

As mentioned, many of these 4002 event ID’s are different with different messages. In the case above it was pointing to Office 365 and not an Exchange Server.

Hope it helps your troubleshooting.

By edward