Comcast Email Server Misconfiguration

Comcast/Xfinity email cannot deliver messages to recipients at diocal.org. Messages bounce back with a DNS configuration / lookup error from Comcast’s outbound mail servers.

This occurs consistently when sending from my Comcast address. Sending to the same recipients from Yahoo Mail succeeds, so the destination domain is reachable and accepting mail.

This appears to be a Comcast outbound SMTP / DNS / MX resolution issue, not a client or device problem. Rebooting or changing mail clients does not apply.

Here is the error message (name edited for privacy):

Your message did not reach some or all of the intended recipients.

      Subject:     test message

      Sent:  1/22/2026 1:40 PM

The following recipient(s) cannot be reached:

      'xxxxxxxxx@diocal.org' on 1/22/2026 1:40 PM

            Server error: '550 5.1.1 <xxxxxxxxx@diocal.org>  Domain unrouteable, possible DNS misconfiguration'

Requesting escalation to Email Operations / Mail Engineering to investigate Comcast’s outbound mail handling for the diocal.org domain.