Poppulo incident
EU and US mail deferrals from Microsoft Exchange
Poppulo experienced a minor incident on September 4, 2026 affecting Email Sending, lasting 1h 53m. The incident has been resolved; the full update timeline is below.
Affected components
Update timeline
- monitoring Sep 04, 2026, 12:22 PM UTC
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
- monitoring Sep 04, 2026, 12:31 PM UTC
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
- resolved Sep 04, 2026, 02:15 PM UTC
This incident has been resolved.