On Fri, 2024-04-19 at 22:55 -0500, Grant Taylor via Mailman-Users wrote:
> Hi,
>
> I'd like some help diagnosing an intermittent DMARC mung failure on
> Mailman 2.1.29.
>
> Some of the time DMARC munging works perfectly fine, and then seemingly
> with no configuration changes, DMARC munging stops working. Then after
> restarting Mailman it may start working again. -- We don't have hard
> consistent data yet.
>
> But we do have a sender that some of the time their system their
> messages come through with "First Last via List"
> <list@listdomain.example> and then other times their messages come
> through with "First Last" <sender@sendersdomain.example>.
>
> No changes on the senders side / infrastructure and no changes on the
> mailing list config / infrastructure.
>
> Does anyone have any recommendations on how to start troubleshooting this?
Does the sender have an internationalized domain name (IDN)? The Utils.py logic
that determines the domain to query for DMARC is based on this code which I've
always wondered how that would work with IDNs.
email = email.lower()
# Scan from the right in case quoted local part has an '@'.
at_sign = email.rfind('@')
if at_sign < 1:
return False
Are you able to reliably dig the sender's DMARC record over and over in a loop
to test the reliability of the sender's DNS, perhaps even testing each of their
nameservers independently? I see folks all the time that have DNS servers out
of sync.
-Jim P.
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