Paubox incident
Microsoft certificate rotation causing higher than average secure message conversion for some outbound customers
Resolved after 1 hour 46 minutes, affecting Outbound Security, on June 17, 2026.
Direct delivery to Microsoft 365 recipients has been restored. Messages sent during the incident were delivered securely via the Paubox Secure Message Center; no mail was lost. Thank you for your patience.
Affected components
Update timeline
- identified Jun 17, 2026, 04:33 PM UTC
Beginning at 6AM UTC today, Microsoft began presenting an updated certificate on some of their hosted mail accounts, and our outbound servers' list of trusted authorities doesn't yet include the new one. As a result, a portion of outbound emails to recipients hosted on Microsoft 365 are currently being routed through the Paubox Secure Message Center instead of delivered directly to the recipient's inbox. Affected recipients receive a notification with a secure link to view the message in our portal. No emails have been lost and no data security has been compromised — the Secure Message Center fallback is operating as designed to protect message content when direct delivery cannot be verified. We are updating the certificate and should have a resolution shortly.
- monitoring Jun 17, 2026, 05:00 PM UTC
We are rolling out a new cert server by server and monitoring.
- resolved Jun 17, 2026, 06:20 PM UTC
Direct delivery to Microsoft 365 recipients has been restored. Messages sent during the incident were delivered securely via the Paubox Secure Message Center; no mail was lost. Thank you for your patience.
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