Some users may be unable to open inbound Secure/Multipurpose Internet Mail Extensions (S/MIME) encrypted email messages

Title: Some users may be unable to open inbound Secure/Multipurpose Internet Mail Extensions (S/MIME) encrypted email messages

User impact: Users may intermittently be unable open some inbound S/MIME encrypted email messages in Exchange Online.

More info: This issue strictly impacts users with the Dynamic Delivery policy enabled.

We've temporarily disabled Dynamic Delivery "for S/MIME messages" while we work to resolve this issue

Additionally, some users see a "Safe Attachments Scan in Progress" message upon opening an encrypted inbound email message.

Current status: Our previously mentioned fix is continuing to deploy across the affected environments and is taking longer than initially expected to complete. As the deployment progresses, many of the affected users should start to see recovery and be able to open previously impacted S/MIME messages. Additionally, we’re exploring options available for expediting this fix deployment so that we can swiftly resolve the issue.

Scope of impact: Some users with Dynamic Delivery enabled attempting to open S/MIME encrypted email messages may be impacted.

Start time: Sunday, November 30, 2025, at 12:00 AM UTC

Next update by: Sunday, December 7, 2025, at 10:00 PM UTC

Title: Some users may be unable to open inbound Secure/Multipurpose Internet Mail Extensions (S/MIME) encrypted email messages

User impact: Users may intermittently be unable open some inbound S/MIME encrypted email messages in Exchange Online.

More info: This issue strictly impacts users with the Dynamic Delivery policy enabled.

We've temporarily disabled Dynamic Delivery "for S/MIME messages" while we work to resolve this issue

Additionally, some users see a "Safe Attachments Scan in Progress" message upon opening an encrypted inbound email message.

Current status: We’ve completed the aforementioned validations for our fix to allow the delivered S/MIME encrypted email messages to be viewed as expected and we’re deploying this fix to the affected environments. We anticipate that the fix will be fully saturated across the environments by our next scheduled communications update. In parallel, our review of the HAR network trace logs has led us to suspect a recent change may not be fully compatible with the Dynamic Delivery policy being enabled and we’re working on testing this theory in our internal environment.

Scope of impact: Some users with Dynamic Delivery enabled attempting to open S/MIME encrypted email messages may be impacted.

Start time: Sunday, November 30, 2025, at 12:00 AM UTC

Next update by: Sunday, December 7, 2025, at 6:30 AM UTC

Title: Some users may be unable to open inbound Secure/Multipurpose Internet Mail Extensions (S/MIME) encrypted email messages

User impact: Users may intermittently be unable open some inbound S/MIME encrypted email messages in Exchange Online.

More info: This issue strictly impacts users with the Dynamic Delivery policy enabled.
We've temporarily disabled Dynamic Delivery while we work to resolve this issue. This action may result in potential delays of up to fifteen minutes for users to receive email messages with attachments. The length of the delay will depend on the attachments associated with the email message.

Additionally, some users see a "Safe Attachments Scan in Progress" message upon opening an encrypted inbound email message.

Current status: We're continuing our review of the HAR network trace logs to progress our root cause investigation while our efforts to validate the fix are ongoing. We'll aim to provide a timeline for the validations to complete by our next scheduled communications update.

Scope of impact: Some users with Dynamic Delivery enabled attempting to open S/MIME encrypted email messages may be impacted.

Start time: Sunday, November 30, 2025, at 12:00 AM UTC

Next update by: Saturday, December 6, 2025, at 6:00 AM UTC

Title: Some users may be unable to open inbound Secure/Multipurpose Internet Mail Extensions (S/MIME) encrypted email messages

User impact: Users may intermittently be unable open some inbound S/MIME encrypted email messages in Exchange Online.

More info: This issue strictly impacts users with the Dynamic Delivery policy enabled.

We've temporarily disabled Dynamic Delivery while we work to resolve this issue. This action may result in potential delays of up to fifteen minutes for users to receive email messages with attachments. The length of the delay will depend on the attachments associated with the email message.

Additionally, some users see a "Safe Attachments Scan in Progress" message upon opening an encrypted inbound email message.

Current status: While we review HTTP Archive format (HAR) network trace logs to isolate the underlying cause of impact, we've disabled Dynamic Delivery to avoid new email messages from becoming impacted. In parallel, we're in the process of validating a fix to allow delivered S/MIME encrypted email messages to be viewed as expected.

Scope of impact: Some users with Dynamic Delivery enabled attempting to open S/MIME encrypted email messages may be impacted.

Start time: Sunday, November 30, 2025, at 12:00 AM UTC

Next update by: Friday, December 5, 2025, at 10:30 PM UTC