Hi,
We upgraded AD Connect from an older version 1.5.3.0 on 2012 R2 to the latest version on Windows 2019. The upgrade was done using a swing migration with a PowerShell script to migrate the AD Connect settings (https://learn.microsoft.com/en-us/azure/active-directory/hybrid/how-to-upgrade-previous-version).
On the day of AD Connect upgrade, everything seemed fine (objects synced and users were accessing O365 as normal). The next day, a number of shared mailboxes stopped working (they were just inaccessible from Outlook and OWA).
On further review, the AD Connect upgrade, post sync seemed to have updated the msExchRemoteRecipientType for several thousand users.
We also noticed thousands of accounts with missing on premise AD attribute values for ms-Exch-Guid.
To fix the issue, we did the following:
- On our Exchange 2013 hybrid server use the Exchange PS cmdlet to set the GUID on-premise to match O365.
- Set the remote mailbox property for shared mailboxes “set-Remotemailbox -Type shared”.
Why did this happen in the first place given we've deliberately exported the settings and kept a like for like configuration?
Thanks