Symptoms
When you run the Get-PublicFolderMailboxDiagnostics cmdlet to view event-level information about a public folder mailbox in Windows PowerShell, you receive the following error message:
[PS] C:\Windows\system32>Get-PublicFolderMailboxDiagnostics -Identity "Public_folder_mailbox"
The process failed to get the correct properties. + CategoryInfo : NotSpecified: (:) [Get-PublicFolderMailboxDiagnostics], TooManyObjectsOpenedException + FullyQualifiedErrorId : [Server=server_name,RequestId=ID_number,TimeStamp= date ] [FailureCategory=Cmdlet-TooManyObjectsOpenedException] 513F4A69,Microsoft.Exchange.Management.MapiTas ks.GetPublicFolderMailboxDiagnostics + PSComputerName : server_nameCause
This issue occurs because the opening message objects exceed the limit when the public folder mailbox has more than 250 Push Sync messages open.
Resolution
Exchange Server 2016
To resolve this issue, install Cumulative Update 10 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
References
Learn about the terminology that Microsoft uses to describe software updates.