EU and US mail deferrals from Microsoft Exchange

This incident has been resolved.

Poppulo Support and Engineering are currently monitoring an increase in deferrals from mailings through protection.outlook.com

Microsoft are advising of an issue with Exchange online leading to "451 4.7.500 Server busy deferrals :


ID: EX1467029
Affected services: Exchange Online
Status: Service degradation
Issue type: Incident
Start time: 4 Sept 2026, 11:19 GMT+1User impact
Users may experience a delay in sending and receiving email messages from external domains in Exchange Online.More info
Users may experience intermittent “Server busy” errors, affecting multiple mailboxes.Scope of impact
This issue impacts users who may be attempting to send and receive email messages from external domains in Exchange Online. This information may be updated as our investigation continues.

Current status
4 Sept 2026, 12:03 GMT+1
Our initial investigation has identified instances where anti-spam protections may be contributing to impact for a subset of users. We are continuing to analyse the behaviour and review service telemetry to better understand the underlying cause and determine the most effective mitigation path

Once the issue is addressed by Microsoft Poppulo will attempt to deliver currently deferred mails.

Poppulo Support

Poppulo Support and Engineering are currently monitoring an increase in deferrals from mailings through protection.outlook.com 

Microsoft are advising of an issue with Exchange online leading to  "451 4.7.500 Server busy deferrals :


ID: EX1467029
Affected services: Exchange Online
Status: Service degradation
Issue type: Incident
Start time: 4 Sept 2026, 11:19 GMT+1User impact
Users may experience a delay in sending and receiving email messages from external domains in Exchange Online.More info
Users may experience intermittent “Server busy” errors, affecting multiple mailboxes.Scope of impact
This issue impacts users who may be attempting to send and receive email messages from external domains in Exchange Online. This information may be updated as our investigation continues.

Current status
4 Sept 2026, 12:03 GMT+1
Our initial investigation has identified instances where anti-spam protections may be contributing to impact for a subset of users. We are continuing to analyse the behaviour and review service telemetry to better understand the underlying cause and determine the most effective mitigation path

Once the issue is addressed by Microsoft Poppulo will attempt to deliver currently deferred mails.

Poppulo Support