So we have a customer that still runs Microsoft Hosted Exchange 2010, so it's not your traditional standard server. Does anyone know if it would be possible to install a second Exchange server in the network and setup coexistence between the two? The goal is to temporary be able to setup this Exchange 2016 server as a frontend for mobile devices and Outlook to connect to while leaving the mailboxes on exchange 2010. In the mean time most of the companies hosted on this server will migrate to a completely new domain with a new Exchange 2019 server or Office365. So the purpose is a temporary frontend server for port 443 and 25. I have not found anything about this online so I assume this is not possible or supported. We have setup coexistence between two servers (Exchange 2010 Standard and Exchange 2016 Standard) but not the Hosted Exchange version.