October 11, 2023 at 12:15PM
Microsoft is currently investigating mail delivery issues in Exchange Online that are causing delays and “Server busy” errors for Microsoft 365 customers worldwide. The problem, which started this morning, may be linked to the enforcement of IP address anti-spam rules. Microsoft is working on formulating a remediation plan and has provided more information in the Microsoft 365 admin center.
From the meeting notes, the key takeaways are:
1. Microsoft is currently investigating Exchange Online mail delivery issues that are causing “Server busy” errors and delays in receiving emails from external organizations.
2. The problems started this morning and are affecting Microsoft 365 customers worldwide.
3. Affected users may encounter delays receiving external email messages and see a “451 4.7.500 Server busy” error message.
4. Microsoft is analyzing sample throttling IPs to determine if the issue with a portion of SOL infrastructure is causing the problem before formulating a remediation plan.
5. The impact is specific to some users served through the affected infrastructure.
6. The ongoing Exchange Online issues are identified under EX680695 in the Microsoft 365 admin center.
7. There is a possibility that the issues are linked to the erroneous enforcement of IP address anti-spam rules for affected customers.
8. Some users are experiencing thousands of emails being added to the outbound queue due to Exchange Online’s spam filter.
9. Microsoft has not confirmed the regions affected or made a public statement about the investigation on their Microsoft 365 Status account on Twitter.
10. The situation is still developing.