Intermittent mail loop bounces

Incident Report for Mailprotector

Resolved

A modification to handling ARC seal authentication was deployed late yesterday evening to handle an outlier situation observed over the past few months. The modification created a mail loop in specific messages that were missing some ARC seal authentication information in the headers. This specific situation caused the emails to look up the MX record for delivery, and those domains with a Shield MX record caused the email to loop.

A fix for this situation was deployed shortly after the mail loop was detected. The fix now accounts for the rare circumstances involving the ARC seal and will gracefully handle mail delivery.

Posted Sep 03, 2025 - 15:18 EDT