EDIT 9/19/2023: This blog post has received significant update.
In this second part of the Demystifying Hybrid Free/Busy, we will cover troubleshooting of Hybrid Free/Busy scenarios, more specifica...
Updated Sep 19, 2023
Version 16.0
Blog Post
MarcoLFrancisco
Microsoft
MicrosoftC-Money the thest OAUth Connectivity if you are using the Intra Org Connector may show aditional error detail.
You can compare working mailbox with not working mailbox:
Test-OAuthConnectivity -Service EWS -TargetUri <On Premises Exchange EWS External URL> -Mailbox <Cloud Mailbox>
Example:
Test-OAuthConnectivity -Service EWS -TargetUri https://mail.contoso.com/ews/exchange.asmx -Mailbox JohnD@contoso.com
If not using OAUth you can use the Test-OrganizationRelationship done from Cloud to On Premises.
You can also check for Geo Locations for Cloud mailboxes, compare and even move:
Administering Exchange Online mailboxes in a multi-geo environment - Microsoft 365 Enterprise | Microsoft Learn
From my experience, socket error generally is due to Nertwork issues. Remote Connectivity Analizer, Checking from OWA if behaviour is the same as in Outlook for the affcted user and check from a computer that is know to work for Free Busy calls from other cloud mailboxes may be good tests.