Microsoft isn't happy you're using unsupported Exchange versions, announces final deadline

Microsoft has put out a rather sternly worded advisory urging customers to complete public folder migrations from legacy versions of Exchange as soon as possible.

Earlier this month, Microsoft announced Exchange Server Subscription Edition (SE), which is the official transition of the product to the Modern Lifecycle Policy, where software is continuously serviced without an end-of-life date, as long as you keep it updated. It also revealed surprising, but brief, Extended Security Updates (ESUs) for Exchange 2016 and 2019. As it winds down support for these products, the company has expressed some displeasure that some customers are using even older and, obviously, unsupported versions of Exchange.

In a blog post, the company has noted that it currently offers migration tools that enable the migration of public folders from on-premise Exchange 2013 or older versions to Exchange Online. This is by design, but Microsoft is now changing its tune on the topic.

Starting from October 1, 2025, customers leveraging Exchange 2010 or older versions of the software will not be allowed to use Microsoft's tools to migrate their public folders to Exchange Online. Microsoft believes that this deprecation will reduce reliance on legacy systems and enhance "long-term service reliability".

Any migrations that are attempted after the aforementioned date will fail, so Microsoft has urged customers to complete their migrations as soon as possible. If customers want to move their data to Exchange Online after October 1, they will first have to upgrade to a newer Exchange version, which is Exchange 2013, but it is important to keep in mind that supported versions are 2016 and 2019.

Microsoft has emphasized in a rather stern tone that it does not encourage using unsupported versions of Exchange Server at all, and it has just put out this advisory because it is aware that public folder migrations from legacy systems are currently active, even though they shouldn't be. Needless to say, customers should upgrade to Exchange Server 2016 or 2019 as quickly as possible, but ideally, they should consider moving to Exchange Server SE at this point, considering that the other two versions are running out of support soon, too.