Microsoft 365 Alert – Service Degradation – Microsoft Teams – Users may have seen Microsoft Teams meeting invitations delivered as “not supported calendar message.ics” attachments – RESOLVED

Announcements Arpan Das

18/03/2026 08:50:00 AM

NHSmail Reference: INC46777144

Microsoft Reference: TM1254548

Issue Status: RESOLVED

Issue Description: Users may have seen Microsoft Teams meeting invitations delivered as “not supported calendar message.ics” attachments.

More info: This affected users sending invitations from organizations within our government infrastructure to non-government organizations; other users were unaffected.

Final Update: 19/03/2026 08:42:00 AM –Microsoft has confirmed through internal testing and with previously affected users that disabling the change remediated impact.

Scope of impact: This incident impacted users receiving Microsoft Teams meeting invitations who may have seen the invitation delivered as a “not supported calendar message.ics” attachment.

Root cause: A recent change intended to improve validation of meeting join links in calendar invitations resulted in valid Microsoft Teams meeting invitations not being processed correctly, causing them to be delivered as unsupported .ics attachments.

Next Steps: Microsoft are investigating how the recent change intended to improve validation of meeting join links in calendar invitations resulted in valid Microsoft Teams meeting invitations not being processed correctly to prevent this problem from happening again.