Microsoft 365 Alert – Service Degradation – Exchange Online – Some users’ encrypted email messages sent from a shared mailbox to external domains may fail to send in Exchange Online – RESOLVED

15/03/2024 08:28:00 AM

NHSMail Reference: INC41947646

Microsoft Reference: EX738185

Issue Status: RESOLVED

Issue Description: Users’ encrypted email messages sent from a shared mailbox to external domains may fail to send in Exchange Online.

Final Update: 18/03/2024 08:42:00 AM – Microsoft have confirmed with a subset of affected users that their additional optimizations were successful at resolving impact, and the issue is remediated for all users.

Scope of impact: This issue impacts some users’ encrypted email messages sent from a shared mailbox to external domains in Exchange Online.

Root cause: A recent change, which was intended to enable the service to perform rule evaluation at the component level, rather than at the email message level, has increased the amount of requests to the service responsible for providing the license to encrypt or decrypt messages, resulting in our traffic management systems to be initialized and failing these requests to the service.

Next steps: Microsoft are reviewing their change testing and validation procedures to identify opportunities to improve impact detection and prevent similar future occurrences.