EX649175: Some users may be unable to send Exchange Online email messages

Microsoft has reported the following issues with Exchange online:

Some users may be unable to send Exchange Online email messages User impact: Users may be unable to send Exchange Online email messages. More info: Affected users may receive the following error “503 5.5.1 bad sequence of commands” Current status: We’re reviewing service monitoring telemetry to isolate the root cause and develop a remediation plan. Scope of impact: Impact is specific to some users who are served through the affected infrastructure.

Latest update:

Some users may be unable to send Exchange Online email messages User impact: Users may be unable to send Exchange Online email messages. More info: Affected users may receive the following error “503 5.5.1 bad sequence of commands” Current status: We’ve identified that a change to the free/busy infrastructure resulted in impact to the Exchange online mail flow infrastructure. We’re identifying a plan to mitigate impact and restore mail flow. Scope of impact: Impact is specific to some users who are served through the affected infrastructure. Next update by: Tuesday, July 18, 2023 at 11:00 AM GMT+1

If you are experiencing the issue please contact our HelpDesk team on 0330 0020 089 and they will be able to check the issue you are having to see if it is related to this issue.

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