Update 6/13/2025: Please see our new blog post for updated timelines of releases as well as additional details on how to get from current versions of Exchange Server to Exchange Server SE: Upgrading ...
Updated Jun 13, 2025
Version 14.0
Blog Post
I don't understand this, can you clarify? We are on 2016 today, will we be permanently blocked to do a legacy upgrade from 2016 to SE after first CU drops? Or do you mean we must upgrade to RTM first, then upgrade to current CU? Or do you mean coexistence as in DAG coexistence, and not Exchange version coexistence? Our Exchange team are stuck in projects and it's straight up impossible to upgrade anything the coming 18 months.
Removal of support for co-existence with all previous versions
At the time CU1 is released, Exchange Server SE will be the only supported version. As all previous versions will be unsupported at that time, Setup in CU1 will block coexistence with anything other than Exchange Server SE RTM or later.