Status impact color legend
- Black impact: None
- Yellow impact: Minor
- Red impact: Major
- Blue impact: Maintenance
[Transactional Email] - world - Delayed email delivery to Microsoft domains (Outlook/Hotmail)
Incident
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Identified
- Start: 2026-11-12 ~18:45 UTC (19:45 CET)
- Impact: Email delivery to Microsoft consumer domains significantly delayed. Backlog of ~2,500 emails pending (incl. short-TTL OTP/auth messages at risk of expiry drops). All sending pools affected; partial delivery continues (8/min vs 25–30/min nominal).
- Symptoms / findings: TCP connection timeouts (SYN unanswered) to Microsoft MX endpoints (52.101.x.x), spread across 10+ sending IPs and all pools. No connection refusals, no SMTP-level throttling — behavior consistent with a Microsoft-side infrastructure degradation, not reputation filtering. Deferrals peaked at ~1,000 MX-unavailable events / 10 min. No other destination domains affected beyond Microsoft consumer properties (+ unrelated, pre-existing Proximus/gtm-tc2 slowness tracked separately).
- External cause: Microsoft 365 / Exchange Online outage, tracked by Microsoft as EX1550543 — acknowledged ~19:37 UTC, fix deployed ~18:30 CET, gradual recovery in progress. Refs: @MSFT365Status, Downdetector (outlook, microsoft-365).
- Mitigation: None applicable (external provider). Emails retry automatically (1-min per-pool MX failure cache + per-email backoff); backlog expected to drain on Microsoft recovery.
- Next steps: Continuous monitoring of MX timeouts, pending backlog and OTP expiry drops; will close once delivery rates return to nominal.
- Impact: Email delivery to Microsoft consumer domains significantly delayed. Backlog of ~2,500 emails pending (incl. short-TTL OTP/auth messages at risk of expiry drops). All sending pools affected; partial delivery continues (8/min vs 25–30/min nominal).
- Symptoms / findings: TCP connection timeouts (SYN unanswered) to Microsoft MX endpoints (52.101.x.x), spread across 10+ sending IPs and all pools. No connection refusals, no SMTP-level throttling — behavior consistent with a Microsoft-side infrastructure degradation, not reputation filtering. Deferrals peaked at ~1,000 MX-unavailable events / 10 min. No other destination domains affected beyond Microsoft consumer properties (+ unrelated, pre-existing Proximus/gtm-tc2 slowness tracked separately).
- External cause: Microsoft 365 / Exchange Online outage, tracked by Microsoft as EX1550543 — acknowledged ~19:37 UTC, fix deployed ~18:30 CET, gradual recovery in progress. Refs: @MSFT365Status, Downdetector (outlook, microsoft-365).
- Mitigation: None applicable (external provider). Emails retry automatically (1-min per-pool MX failure cache + per-email backoff); backlog expected to drain on Microsoft recovery.
- Next steps: Continuous monitoring of MX timeouts, pending backlog and OTP expiry drops; will close once delivery rates return to nominal.
This incident affects: Elements - Products (Transactional Email).