Some users may be unable to open inbound Secure/Multipurpose Internet Mail Extensions (S/MIME) encrypted email messages
ID: EX1192586
Issue type: Incident
|
|
|---|
|
|
Impacted services
Exchange Online
|
|
|---|
|
|
Details
Title: Some users may be unable to open inbound Secure/Multipurpose Internet Mail Extensions (S/MIME) encrypted email messages
User impact: Users may have been unable to open some inbound S/MIME encrypted email messages in Exchange Online.
More info: This issue affected users with the Dynamic Delivery policy enabled.
We previously disabled Dynamic Delivery "for S/MIME messages" while we worked to resolve this issue, which has since been re-enabled.
Final status: We've confirmed that the configuration has been updated and validated this action has remediated the impact using service telemetry.
Scope of impact: Some users with Dynamic Delivery enabled that were attempting to open S/MIME encrypted email messages may have been impacted.
Start time: Sunday, November 30, 2025, at 12:00 AM UTC
End time: Monday, December 8, 2025, at 10:00 AM UTC
Root cause: A recent service update that intended to introduce a new Microsoft Defender for Office 365 feature incorrectly marked S/MIME messages for delivery, resulting in impact.
Next steps:
- We're continuing our analysis of the impacting configuration change to better identify and prevent similar issues in the future.
This is the final update for the event.
|
|
|---|
|
|
|
|
Did you find this email helpful?
Yes
No
|
|
|---|
|
|
To customize what’s included in this email, who gets it, or to unsubscribe, set your Service health preferences. If you are receiving this email because your Admin added you as a recipient, please contact your Admin to unsubscribe.
|
|
|---|
|
|
|
|
|
