Microsoft 365 Alert – Service Degradation – Exchange Online – Some users’ outbound email messages may display an unexpected sender name in Exchange Online – RESOLVED

Announcements Shagufta Naaz

24/03/2026 08:42:00 AM

NHSmail Reference: INC46780510

Microsoft Reference: EX1259159

Issue Status: RESOLVED

Issue Description: Some users’ outbound email messages may display an unexpected sender name in Exchange Online.

More info: When affected users sent email to external recipients, the sender name shown may have been the mailbox DisplayName instead of the configured SimpleDisplayName.

Final Update: 24/03/2026 08:42:00 AM – Microsoft’s has confirmed through internal testing that impact is no longer occurring. While no further outbound messages should be impacted, email messages that were already sent with the unexpected sender name will continue to show the sender name used when originally sent.

Scope of impact: Some users sending email to external recipients in Exchange Online may have been impacted.

Root cause: A recent service update introduced new outbound mail behavior that caused Exchange Online to stop honoring the configured SimpleDisplayName in some outbound email scenarios, resulting in impact.

Next steps: Microsoft are reviewing our update testing and validation methods to better identify issues such as this prior to deployment so we can prevent similar impact in the future.