Mailboxes will be moved from Exchange Server 2010 to Exchange Server 2013 for Office 365 dedicated and ITAR customers. The main Windows Remote PowerShell endpoint (usually https://mail.contoso.com/powershell) will connect to an Exchange 2010 client access server (CAS) during the upgrade process.
An alternative endpoint should be used when you change the properties of a mailbox in Exchange Server 2013. The alternative Exchange 2013 endpoint is configured during the pre-configuration steps of the migration and may resemble one of the following:
After all the mailboxes are moved to Exchange Server 2013, the default endpoint will connect to an Exchange 2013 CAS, and the alternative endpoint is not required.