[Mailman-Users] Recent trouble with DMARC Munging

Mark Sapiro mark at msapiro.net
Mon Jan 16 13:23:47 EST 2017

On 01/15/2017 08:58 PM, Scott Neader wrote:
> When yahoo.com or AOL.com users post to our
> lists, the Munging is not working.  When I query for a DMARC record from
> the mail server, it can see the record, so I think it's not a resolver
> issue.
> I'm really stumped... any pointers/ideas on where to look would be greatly
> appreciated!

It seems you have access to the Mailman server, so look in Mailman's
error log. If you see messages like

DNS lookup for dmarc_moderation_action for list <listname> not available

it means at the time Mailman was last (re)started, the import of
dns.resolver failed. This is unlikely as it had been working.

Also look for messages beginning

DNSException: Unable to query DMARC policy for ...

These should be self explanitory.

Also look in Mailman's vette log. There should be messages like

<listname>: DMARC lookup for <email> (_dmarc.<domain>) found p=reject ...

for each post from AOL, Yahoo, etc. Presumably, there will be none of
these since munging stopped.

Let us know what you find. Note that if you are seeing the

DNS lookup for dmarc_moderation_action for list <listname> not available

messages, restarting Mailman may fix it. Also, in this case try

python -c "import dns.resolver"

to see if it reports any error.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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