Microsoft 365 Alert – Service Degradation – Exchange Online – Users’ inbound and outbound email delivery may be delayed for 15 minutes or longer in Exchange Online – RESOLVED

18/07/2023 08:37:00 AM (GMT)

NHSmail Reference : INC37067770

Microsoft Reference : EX648815

Issue Status : RESOLVED

Issue Description : Users’ inbound and outbound email delivery may be delayed for 15 minutes or longer in Exchange Online.

More info : The issue isn’t client-specific, thus this impact may occur in all Exchange Online connection methods.

Final Update : 19/07/2023 08:40:00 AM – Microsoft confirmed that the previously communicated rerouting update to the free/busy CFMs wouldn’t fully remediate the issue as messages may requeue again. After monitoring the mail queues, they confirmed that the messages have been reprocessed and new messages are sending within the expected timeframe.

Scope of impact : This issue may affect any user sending or receiving mail in Exchange Online.

Root cause : A recent code change related to our free/busy publishing APIs has resulted in an influx of Control Flow Messages (CFMs), which are sent during certain free/busy operations such as calendar replication, to be sent for other instances where CFMs are not necessary. This is resulting in a spike in messages on Exchange Online infrastructure, which is resulting in message queuing.

Next steps : Microsoft are continuing to review the free/busy API changes and CFMs to better understand why the spike in unnecessary messages occurred to prevent similar occurrences from happening again in the future.