Duplicate Exchange Online and Exchange Server Mailboxes

With a hybrid Exchange Online deployment, where you have Exchange Server on-premises and Exchange Online configured in the cloud, and utilising AADConnect to synchronize the directory, you should never find that a synced user object is configured as both a mailbox in the cloud and a mailbox on-premises. When Active Directory is synced to Azure Active Directory, the ExchangeGUID attribute for the on-premises user is synced to the cloud (assuming that you have not do […]