[Transactional Email] - world - Delayed email delivery to Microsoft domains (Outlook/Hotmail)

Start: 2026-11-12 ~18:45 UTC (19:45 CET)

Impact: Some emails can take up 1 hour to be delivered.

Cause: External. Microsoft 365 / Exchange Online outage

Mitigation: Continuous monitoring of MX timeouts

The Microsoft incident is still ongoing, with no estimated recovery time available.

The growing backlog of emails to Microsoft is putting pressure on our delivery queue and could delay emails sent to other providers.

To protect delivery performance for all other providers, we will cancel some pending emails addressed to Microsoft. If the incident exceeds our retry window, some remaining emails may also bounce. A bounce event will be generated for each affected email.

Cancelled or bounced emails can be resent once Microsoft services are restored.

In order to protect the current delivery to other email providers, and in addition with the previous action, we decided to refuse emails in destination to Microsoft's servers. The emails will be rejected with a "550 5.7.1 The recipient domain <domain> is temporarily not supported" SMTP message. The same behavior is expected on API side.