Issues with different Exchange Server versions

Different versions of Exchange Server have issues when you modify mailboxes on a server of one version from a powershell session on a server with a different version.

Preferred servers

Preferred servers let you specify which Exchange servers are used to execute requests.

There is no API for managing Exchange servers. Exchange servers are managed by using powershell cmdlets. The required cmdlets are only available on the Exchange servers. The adapter must use a remote powershell connection to one of the servers to execute the cmdlets to process a request.

The adapter uses the concept of preferred servers for both Exchange and Skype for Business.

When a request comes in, the adapter must connect to a remote server to execute the request. By default, it does an LDAP search into AD to find the servers, then tries to connect. It uses the first server that it can connect with. If preferred servers are specified, the adapter will try to connect with those servers first. Setting the exclusive flag to TRUE will force the adapter to only use the preferred servers.

Remember that the preferred servers are where the request is executed. This has nothing to do with where mailboxes are created. The account attribute erMailboxStore specifies the mail database which is not necessarily on the preferred server.