Outage in Microsoft 365
External users’ replies to encrypted email messages may not be delivered in Exchange Online
Resolved Minor
October 29, 2026 - Started 5 days ago
- Lasted 1 day
Incident Report
Summary AI Generated
External users were unable to reply to encrypted emails in Exchange Online for approximately 30.5 hours beginning October 29, 2026. The issue was caused by an anti-spam rule incorrectly triggering on internal domains associated with encrypted message delivery, placing them on an outbound banned sender list. Microsoft resolved the issue by applying an exclusion for the affected domains to remove them from that list.
Title: External users’ replies to encrypted email messages may not be delivered in Exchange Online
User impact: External users’ replies to encrypted email messages may not be delivered in Exchange Online.
Current status: We're investigating a potential issue with Exchange Online and checking for impact to your organization. We'll provide an update within 30 minutes.
User impact: External users’ replies to encrypted email messages may not be delivered in Exchange Online.
Current status: We're investigating a potential issue with Exchange Online and checking for impact to your organization. We'll provide an update within 30 minutes.
Components affected
Exchange OnlineTrusted by 1,000+ teams
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Latest Updates ( sorted recent to last )
4 days ago - at 10/30/2026 09:59PM
Title: External users’ replies to encrypted email messages may not be delivered in Exchange Online
User impact: External users’ replies to encrypted email messages may not be delivered in Exchange Online.
Current status: We’ve identified that an anti-spam rule is being triggered on internal domains associated with encrypted message delivery, resulting in impact. We’re applying an exclusion to these affected domains to exclude them from our outbound banned sender list to remediate impact.
Scope of impact: This issue may affect any users utilizing encrypted messages.
Start time: Thursday, October 29, 2026, at 4:00 PM UTC
Root cause: An anti-spam rule is being triggered on internal domains associated with encrypted message delivery, resulting in impact.
Next update by: Saturday, October 31, 2026, at 12:30 AM UTC
4 days ago - at 10/30/2026 09:47PM
Title: External users’ replies to encrypted email messages may not be delivered in Exchange Online
User impact: External users’ replies to encrypted email messages may not be delivered in Exchange Online.
Current status: We're investigating a potential issue with Exchange Online and checking for impact to your organization. We'll provide an update within 30 minutes.
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