[Clo-devel] Modern internet mail rules and mailing list Subject rewriting
ehuels at gmail.com
Wed Feb 4 12:46:16 UTC 2015
Monitoring the mail system, I've found that Google still has us rate
limited. Trying to understand why, I've come up with the following reason:
Google verifies DKIM as part of their criteria for identifying SPAM. We
sign our outgoing mail, so, there shouldn't be a problem. However, some
mail *already* has a DKIM signature. Still no problem, but most mailing
lists change the Subject: line by prepending the mailing list name.
Now *that*'s a problem: it invalidates the pre-existing signature! So,
simply strip the old DKIM headers, you might say. That will make the
problem go away. Well, in fact it probably doesn't: domains which use DKIM
can also state a policy that all mail from the domain should be signed.
Stripping the DKIM signature makes the mail invalid with respect to that
policy, again triggering the SPAM rules.
My conclusion: we have to stop munging the Subject: line in the mailman
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