Microsoft pulled its November 2024 Exchange security updates that it released earlier this month for Patch Tuesday due to them breaking email delivery.
This decision came after there were reports from admins saying that email had stopped flowing altogether.
The issue affects Microsoft Exchange customers who use transport rules, or mail flow rules, as well as data loss protection rules. The mail flow rules filter and redirect emails in transit, while the data loss protection rules ensure that sensitive information isn’t being shared via email to an outside organization.
According to Microsoft, some customers found that the mail flow rules stopped periodically after they installed the update. It is now advising admins who are noticing this issue to uninstall the November security updates entirely until they’re re-released.
“We are continuing the investigation and are working on a permanent fix to address this issue,” Microsoft stated in an update regarding the issue. “We will release it when ready. We have also paused the rollout of November 2024 SU to Windows / Microsoft Update. Customers who might not use Transport or DLP rules and did not run into the issue with rules, can continue using the November SU update.”