[Mailman-Developers] Fixing DMARC problems with .invalid munge

[Stephen J. Turnbull]

John R Levine writes:

 > Isn't there code in 2.18 to check for DMARC problems to catch messages on 
 > the way in?  I'd think you could adapt that.

I'm not sure what "on the way in" means, but 2.1.18 does have code to
catch a p=reject record and handle it just once per post.  The OP
can't use 2.1.18.  It also requires a 3rd-party module (easily
available on PyPI, and probably that doesn't bother the OP, but it
does bother some people).

I think I suggested a cache in Mailman earlier, but as Mark suggested
a local caching nameserver might be just as effective, since mail
handling nowadays requires a ton of DNS lookups aside from DMARC.
Caches are tricky beasts to manage, especially when somebody else
might decide to invalidate them without telling you.