DIAGNOSTIC PLAYBOOK
A mailing list changed the subject and broke DKIM
Mailing lists can alter signed fields or body content when adding subject tags and footers. Compare the original with the redistributed version to find which transformation affected verification.
HealthCheck Email editorial team · · Examples are illustrative
How to investigate
- Obtain a controlled direct copy and a copy delivered through the list.
- Inspect the original signature's signed-header list and compare the raw subject and body.
- Review the list's supported signing, From handling and ARC behavior with its administrator.
What this looks like
ILLUSTRATIVE EXAMPLE
A list prepends a topic label to a signed Subject field. The original signature may fail even though the message came from a legitimate subscriber.
A mistake to avoid
Do not turn off domain authentication to accommodate one list. Investigate the intermediary's supported behavior and the receiver's handling.
Keep the result in context
Inspect the original raw message rather than a forwarded screenshot. Headers can contain private addresses, message identifiers and routing information, so redact a separate copy before sharing. Give the most weight to results added by your own trusted receiving infrastructure.
Take the next step
Use the related check to gather evidence, then compare it with the affected message or service. Keep the result and time with your notes so a later change can be distinguished from the original problem.
Sources and further reading
The protocol references below explain the underlying behavior. Your sending or DNS provider supplies the account-specific settings for its service.