Microsoft 365 Alert – Service Degradation – Exchange Online – Recently migrated on-premises users may be unable to send email – RESOLVED

30/06/2023 08:55:00 AM (GMT)

NHSmail Reference : INC36720607

Microsoft Reference : EX615012

Issue Status : RESOLVED

Issue Description : Recently migrated on-premises users may be unable to send email.

More info : Impacted users receive a Non-Delivery Report (NDR) that references a “MaxSendSize” issue.

In order to correct the issue for currently affected users, admins will need to do the following:

1) Use “Get-Mailbox” to check the current MaxSendSize. If it is set to 0 unintentionally, that user may need to be fixed.

2) Set the “Set-Mailbox” cmdlet on the recently migrated user’s cloud object to set the MaxSendSize to unlimited, which should allow mail to flow.

Microsoft’s fix deployment will only prevent further impact from occurring. The above process is necessary to fully restore mail flow for already affected users.

Final Update : 19/07/2023 15:46:00 PM – Microsoft confirmed that the deployment of the fix is complete, and after an extended monitoring period, their telemetry shows the issue has been remediated.

Scope of impact : Any recently migrated on-premises users may be unable to send email and may receive a NDR.

Root cause : A recent service update that was intending to improve our support of third-party cloud cache quota limits has resulted in impact.

Next steps : Microsoft are reviewing their update procedures to understand why recently migrated from Exchange Online to on-premises users was”t caught during the testing phase. This will allow them to drive service improvements proactively, identifying similar issues in the future and improve their update testing procedures.

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