Live status of all services Incident · resolved

External users’ replies to encrypted email messages may not be delivered in Exchange Online

Exchange Online EX1532233

External users’ replies to encrypted email messages may not have been delivered in Exchange Online.

Status
Service restored
Feature
Mailflow - delayed delivery from Internet
Region
Not specified (all regions)
Started
Oct 29, 2026, 17:00 CET
Resolved
Oct 30, 2026, 23:11 CET
Duration
30 h 11 min

Scope of impact

This issue may have affected any users utilizing encrypted messages.

Root cause

An anti-spam rule was being triggered on internal domains associated with encrypted message delivery, resulting in impact.

Next steps:
- We're reviewing our anti-spam rules to better understand why they were triggered on the affected domains and prevent similar future occurrences.

This is the final update for the event.

Final status

We've applied an exclusion to the affected domains and confirmed after monitoring service telemetry that errors associated with failed deliveries have ceased, confirming impact resolution.

Timeline

Every update Microsoft posted for this issue, newest first.

  1. Oct 30, 2026, 23:21 CET

    We've applied an exclusion to the affected domains and confirmed after monitoring service telemetry that errors associated with failed deliveries have ceased, confirming impact resolution.

  2. Oct 30, 2026, 22:59 CET

    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.

  3. Oct 30, 2026, 22:47 CET

    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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