Please see Update on Transport Enforcement System in Exchange Online for an updated timeline.
2/20/2025: Please note that thottling/blocking has now been enabled for all versions of Exchange Server...
Updated Feb 20, 2025
Version 8.0
Blog Post
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Throttling and Blocking Email from Persistently Vulnerable Exchange Servers to Exchange Online
Hi ScottSchnoll KevinShaughnessy Nino_Bilic
I'm just after some clarification.....we have E2k10 on-premise still (don't get me started) to support 3 x mailboxes which are used some Line Of Business applications.
All our other mailboxes are in Exchange Online.
The mail from these mailboxes on E2k10 eventually makes it's way to O365 across an Exchange Online inbound connector type of OnPremises.
Is Exchange Online going to look back in the message headers and somehow determine that the originating server of the email is E2k10 and start to block those emails?
Or is Exchange Online only ever going to look at the last hop (the machine actually making the connection) to O365 and block based on it's version?