Certain messages rejected in the CH instance of seppmail.cloud

A change effected May 18 2026 at 23:30 CET introduced a regression error which caused certain messages to be rejected with a message of

50 5.7.1 Could not verify X-OriginatorOrg: header not found

After the negative effect was observed, the change was rolled back and mail processing resumed as intended.

The incident affected messages that were routed through an outbound processing facility (“Switch Lausanne”) via IPv6 from M365-hosted customers. It affected customer domains with “inline” integration (ie, customers with “parallel” integration were not affected).

A deeper analysis of the root cause is currently ongoing and we will take measures to a) avoid such an error and to b) mitigate the customer impact faster.

We apologize for the inconvenience caused.

(Updated 2026-05-19 11:40 with clearer information about the scope of affected messages and corrected the severity from minor to major incident.)