September 21, 2023 - Here's the most recently updated timeline.
On March 23, we announced that we would be enabling a transport enforcement system in Exchange Online to address the problem of email sent to Exchange Online from unsupported and unpatched Exchange servers.
As we mentioned in our original announcement, we are starting with a very small subset of servers: Exchange 2007 servers that connect to Exchange Online over an inbound connector type of OnPremises. We have specifically chosen to start with Exchange 2007 because it is the oldest version of Exchange from which you can migrate in a hybrid configuration to Exchange Online, and because these servers are managed by customers we can identify and with whom we have an existing relationship.
Customers with servers in this configuration that send mail to Exchange Online will see a new mail flow report in the Exchange admin center that provides details to a tenant admin about any unsupported or out-of-date Exchange servers in their environment that are connecting to Exchange Online to send email.
Delay of Reporting to First Set of Customers
Our original plan was to make this report available to the first set of customers with servers in scope by the end of this month. However, we are still finalizing the report and finishing up some other related engineering activities. As a result, we are going to delay the release of the report to the first set of customers by 1 month. The report is now expected to be released to the first set of customers on June 23, 2023.
Updated Expected Timeline for other Exchange Server Versions
With reporting now targeted for June 23, 2023 for the first set of customers, the overall timeline has also been adjusted by 30 days. Our new expected timeline for existing Exchange Server versions is below:
As a reminder, for all versions listed above, we're only evaluating the connecting server, and only if it sends mail over an inbound connector type of OnPremises. All other configurations are not yet in scope.
As always, we want and welcome your feedback. Leave a comment on this post if you have any questions or feedback you’d like to share.