We are excited to announce the general availability of Exchange Server Subscription Edition (SE). This release continues Microsoft’s long tradition of enabling customers to provide enterprise email s...
Updated Aug 06, 2025
Version 5.0
Blog Post
Does the release of SE RTM change anything to transport enforcement for the hybrid connectors (throttling and blocking for OnPremises connectors)?
If I remember correctly, in terms of transport enforcement, only the current version of Exchange (including the current and 2 previous CU's) AND the most recent CU of the previous Exchange version is considered 'safe', so today this would now be limited to SE RTM (current version) + 2019 CU15 (last CU of previous version) only.
Specifically:
- Will mail still sent from Exchange 2016 be accepted by Exchange Online today, or will they start being reported as out-of-date (and eventually throttled and blocked)?
- When will we start seeing reporting/throttling/blocking for Exchange 2019 (and 2016 if the above doesn't apply)? Is it Oct 27 (=end of support), the release of SE CU1, or CU2 (when coexistence ends)?
Nino_Bilic
Microsoft
MicrosoftNo change.
Throttling / blocking is not a “you need to be on the latest build” enforcement system. So far, we have had a generous number of builds that are not considered “persistently vulnerable”. Our business is not throttling or blocking emails.
Throttling / blocking builds are decided on by humans after triaging the security payload that we have released in the past. In the case of a really high severity vulnerability (think of something like HAFNIUM from a few years ago) - I expect that we would bring the “persistently vulnerable” bar much closer to the present time sooner, than if we did not have such things. Therefore, there is no set “amount of time” that throttling / blocking covers, because that time can change.
Do we have plans to throttle / block fully up to date E2016/E2019 in November 2025? No. Could there be a set of circumstances that makes it so we block them somewhat soon after they go out of support? Possibly… but realize that if that happens, there are serious security vulnerabilities that we are dealing with, and everyone really needs to be updating their servers ASAP. There is no "calendar schedule" that decides this.
Also remember that the only servers that are throttled / blocked are the ones with connectors to Exchange Online. Update those.