Assume that you apply Cumulative Update 1 for Microsoft Exchange Server 2013 in your organization together with Microsoft Exchange Server 2010 Service Pack 3 (SP3). Then, Active Directory changes the file version of the inproxy.dll file that is based on the ServerSchema.VersionNumber value to point to the Exchange 2013 version. In this situation, the first time you run a cmdlet to configure mailboxes from Exchange 2010 PowerShell will take longer to return the result compared to other times that you run the cmdlet.
Note After you run the iisreset command or recycle the application pool on the Exchange 2010 server, this issue occurs again.
This issue occurs because Active Directory updates the inproxy.dll file to the Exchange 2013 version. However, the Exchange 2013 Mailbox server does not share the inproxy.dll file. Exchange 2010 cannot copy the latest inproxy.dll file from Exchange 2013, and then Exchange 2010 has to cycle through all available servers for the latest inproxy.dll file. Therefore, it takes a longer time than expected.
To resolve this issue, install the following cumulative update:
2892464 Description of Cumulative Update 3 for Exchange Server 2013
To work around this issue, share the inproxy.dll file manually with the read-only permission to authenticated users on the Exchange 2013 Mailbox server. By default, the file is located in the following path:
C:\Program Files\Microsoft\Exchange Server\V15\Mailbox\address\smtp\amd64
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.