Some users’ outbound email messages may display an unexpected sender name in Exchange Online

Title: Some users’ outbound email messages may display an unexpected sender name in Exchange Online User impact: Users’ outbound email messages may have displayed 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 status: We've 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. Start time: Thursday, March 5, 2026, at 10:00 PM UTC End time: Monday, March 23, 2026, at 6:40 PM UTC 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: - We're 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. This is the final update for the event.

Title: Some users’ outbound email messages may display unexpected sender name in Exchange Online User impact: Users’ outbound email messages may display unexpected sender name in Exchange Online. More info: When affected users send email to external recipients, the sender name shown may be the mailbox DisplayName instead of the configured SimpleDisplayName. Current status: We’ve completed reverting the offending update and are reaching out to some users who initially reported the issue to validate that the impact is remediated. Scope of impact: Some users sending email to external recipients in Exchange Online may be impacted. This information may be updated as our investigation continues. 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 update by: Tuesday, March 24, 2026, at 5:00 AM UTC

Title: Some users’ outbound email messages display unexpected sender name in Exchange Online User impact: Users’ outbound email messages display unexpected sender name in Exchange Online. More info: When affected users send email to external recipients, the sender name shown may be the mailbox DisplayName instead of the configured SimpleDisplayName. Current status: We’re confirming whether the update identified is causing impact and whether this can be safely reverted as a mitigation step. In parallel, we’re evaluating alternative mitigation options. We’ll provide an update once a mitigation path is confirmed. Scope of impact: Some users sending email to external recipients in Exchange Online may be impacted. This information may be updated as our investigation continues. 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 update by: Monday, March 23, 2026, at 8:30 PM UTC

Title: Some users’ outbound email messages display unexpected sender name in Exchange Online User impact: Users’ outbound email messages display unexpected sender name in Exchange Online. More info: When affected users send email to external recipients, the sender name shown is the mailbox DisplayName instead of the configured SimpleDisplayName. Current status: We’ve identified that 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. We're assessing available mitigation options to safely resolve impact. Scope of impact: Your organization is affected by this event, and some users sending email to external recipients in Exchange Online are impacted. This information may be updated as our investigation continues. 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 update by: Monday, March 23, 2026, at 2:00 PM UTC

Title: Some users’ outbound email messages display unexpected sender name in Exchange Online User impact: Users’ outbound email messages display unexpected sender name in Exchange Online. More info: When affected users send email to external recipients, the sender name shown is the mailbox DisplayName instead of the configured SimpleDisplayName. Current status: We’re reviewing message headers from affected users and continuing to examine recent code changes to identify a potential regression. We’ll share additional updates as soon as more information is available. Scope of impact: Your organization is affected by this event, and some users sending email to external recipients in Exchange Online are impacted. This information may be updated as our investigation continues. Next update by: Monday, March 23, 2026, at 12:00 PM UTC

Title: Some users’ outbound email messages display unexpected sender name in Exchange Online User impact: Users’ outbound email messages display unexpected sender name in Exchange Online. More info: When affected users send email to external recipients, the sender name shown is the mailbox DisplayName instead of the configured SimpleDisplayName. Current status: We’re investigating reports that outbound email isn’t honoring SimpleDisplayName, even though the remote domain and mailbox settings are configured correctly. We’ve reproduced the issue internally and are reviewing recent code change history in the outbound mail flow pipeline to identify a potential regression. Scope of impact: Your organization is affected by this event, and some users sending email to external recipients in Exchange Online are impacted. This information may be updated as our investigation continues. Next update by: Monday, March 23, 2026, at 10:00 AM UTC