Microsoft 365 Alert – Service Degradation – Exchange Online – Users may be unable to download or open email attachments in Outlook on the web – RESOLVED

Announcements Shagufta Naaz

15/04/2026 8:39:00 AM

NHSmail Reference: INC46799554

Microsoft Reference: EX1275040

Issue Status: RESOLVED

Issue Description: Users may be unable to download or open email attachments in Outlook on the web.

More info: This issue may intermittently impact some users who attempt to access the Exchange Online service through the Outlook mobile apps or the new Outlook for Mac desktop client.

Final Update: 20/04/2026 9:07:00 AM– Microsoft are continuing their efforts of restarting the affected portion of infrastructure, which they anticipate will be complete by their next scheduled update. Afterwards, they will monitor internal telemetry to validate if the impact is remediated or if additional actions are needed to resolve the underlying issue.

Scope of impact: Some users attempting to download or open email attachments in Outlook on the web are impacted. This information may be updated as our investigation continues.

Next Steps: Microsoft are reviewing the affected portion of Outlook on the web infrastructure to determine how the authentication issue was introduced, so that they can prevent similar instances of impact from occurring in the future.