🔒Microsoft Blocks Email from Outdated Exchange Servers to Exchange Online
Your Exchange Server 2016/2019 needs an update
TL;DR
Microsoft is blocking email from Exchange Server 2016 and 2019 installations that haven't been updated to the final public update baseline from October 2025. This affects only servers sending email through an inbound OnPremises connector.
Microsoft is blocking email from Exchange Server 2016 and 2019 installations that haven't been updated to the final public update baseline from October 2025. This move is aimed at ensuring security and compliance, affecting only servers sending email through an inbound OnPremises connector. If your organization relies on hybrid deployments or applications that depend on these servers for email, you need to update to avoid disruptions. The baseline update was released a year ago, and all organizations should have already applied it. This change gives administrators advance notice to avoid future disruptions.
Key Points
Microsoft blocks email from Exchange Server 2016 and 2019 installations not updated to the final public update baseline from October 2025.
The baseline update was released in October 2025, almost a year ago.
This policy affects only servers sending email through an inbound OnPremises connector to Exchange Online.
Organizations may retain on-premises Exchange servers for hybrid deployments or applications that depend on them.
Administrators should balance the need to apply security patches promptly against the risk of introducing problems.
Why It Matters
If you're running Exchange Server 2016 or 2019 and sending email to Exchange Online through an inbound OnPremises connector, your server needs to be updated to the final public update baseline from October 2025. This update was released almost a year ago, and the policy change gives you advance notice to avoid disruptions. Failing to update could lead to blocked email and compliance issues.
Frequently Asked Questions
Why does this matter?
If you're running Exchange Server 2016 or 2019 and sending email to Exchange Online through an inbound OnPremises connector, your server needs to be updated to the final public update baseline from October 2025. This update was released almost a year ago, and the policy change gives you advance notice to avoid disruptions. Failing to update could lead to blocked email and compliance issues.
What happened?
Microsoft is blocking email from Exchange Server 2016 and 2019 installations that haven't been updated to the final public update baseline from October 2025. This affects only servers sending email through an inbound OnPremises connector.
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