Symptoms
Currently, the Start-MailboxAssistant cmdlet is not available in the Exchange Management Shell (EMS) in Microsoft Exchange Server 2019 until you add a plug-in. This update makes the Start-MailboxAssistant cmdlet available without having to add the plug-in.
Resolution
To fix this issue, install the following update:
Cumulative Update 11 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019
References
Learn about the terminology that Microsoft uses to describe software updates.
