Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may see an unexpected “[EXTERNAL]” tag appended to the subject line of some incoming email messages – RESOLVED

Announcements Sourav Nandi

23/07/2025 09:10:00 AM

NHSmail Reference: INC46586275

Microsoft Reference: EX1120259

Issue Status: RESOLVED

Issue Description: Some users may see an unexpected “[EXTERNAL]” tag appended to the subject line of some incoming email messages.

Final Update: 23/07/2025 11:14:00 AM – Microsoft have discovered that a recent update intended to enhance their anti-spam filtration process inadvertently caused impact. They have since reverted the update and confirmed through service telemetry and feedback from affected users that the issue has been resolved.

Scope of impact: Impact is specific to some users who see an unexpected “[EXTERNAL]” tag appended to the subject line of some incoming email messages.

Next Steps: Microsoft are reviewing their anti-spam update procedures to help prevent similar problems in the future.