Update 8/13/2026: This retirement is now complete, please see Released: August 2026 Exchange Server Security Updates | Microsoft Community Hub. For customers who do not have access to August 2026 Exc...
Updated Aug 13, 2026
Version 3.0
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I assume this August update will be SE CU1 (not a security update), and that if you are still running Exchange 2016/2019 you will need to manually disable this as per the steps outlined above?
Additionally, we had a couple users who were stuck in light mode / the options to disable it via the browser no longer works. Our fix for this was to run the following command:
Set-CasMailbox -Identity xxx -IsOptimizedForAccessibility $false
We disabled OWA Light after the June Mitigations made it unusable, and users, like you mentioned, could not disable it themselves. Thankfully one of our other admins found the same solution to disable it for them, and I could use that to disable OWA Light for the remaining mailboxes still using it.
I had honestly forgotten OWA Light even was a thing, so good riddance.