I had and issue where O365 Share Mailboxes disappeared after a minute or so. After a bit of googling, I found this solution
Configure one of the following registry subkeys as follows:
HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\Autodiscover
DWORD: ExcludeLastKnownGoodUrl
Value: 1
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\x.0\Outlook\Autodiscover
DWORD: ExcludeLastKnownGoodUrl
Value: 1
Note: The x.0 place holder represents your version of Office (16.0 = Office 2016, Office 365 and Office 2019, 15.0 = Office 2013).
Taken from this MS Technote (Kudos to Eoin for the updated link)…..
Hi,
I have an on-premise exchange but also a 365 license and my mailboxes kept vanishing after a minute.
This fix worked a treat for me.
Thanks.
Thanks!!
Hey Heads up !
Your reference link doesnt work. Here is the updated link:
https://learn.microsoft.com/en-us/troubleshoot/outlook/profiles-and-accounts/cannot-connect-web-service-not-working-migrated-to-office-365