[Linux-aus] PSA: Messages sent through LA mailing lists being classified as SPAM

[Joel W. Shea]

On Thu, Jan 14, 2016 at 04:55:55PM +1100, Russell Coker wrote:
>
> [...] Finally Mailman doesn't preserve headers it rewrites them and
> uses a different method of header folding. [...] Fixing this would
> require some significant changes in the Mailman code, I believe it
> uses library code for this which makes it even harder. [...]

I've confirmed the above, it uses an upstream library that appears to
refold the headers after parsing and re-writing them. I'm not sure how
difficult it would be to fix this, only because lots of software may
already depend on the current behaviour.

> [...] OpenDKIM uses tabs and both OpenDKIM and libmail-dkim-perl
> expect tabs when it receives mail, Mailman refolds it with spaces
> instead and those programs can't validate the mail (I'm not aware of
> any DKIM checker that accepts spaces). [...]

Although I haven't tested directly, I believe Mailman may only break
DKIM signatures where the canonicalization method is "simple" (rather
than "relaxed"), unfortunately this is both the default setting for
OpenDKIM, and also where it's not explicitly specified in the header.

> If you use the from_is_list feature then messages will have the
> following change: -From: Russell Coker <russell at coker.com.au> +From:
> Russell Coker via linux-aus <linux-aus at lists.linux.org.au>

Please DO NOT set from_is_list, as this will annoy users, use
dmarc_moderation_action instead. (as below)

> Then the Linux Australia server can sign the messages with it's own
> DKIM signature.

Do you still need to re-write the From: header just to sign a message?

> Mailman 2.1.8 (the version used here) has a new option
> dmarc_moderation_action.  That option means that all DKIM signed
> messages (not DMARC messages regardless of what is indicated) will be
> treated differently (wrapped, From munged, etc).

My testing revealed that messages would be munged when there was a DMARC
record, although I did not test DKIM without DMARC, as you have done.

> I think that dmarc_moderation_action is a really bad idea as it means
> that some of the messages will be processed one way and some processed
> another way.

Perhaps, I understand the desire for consistency, but I disagree that
it's a bad idea.

> Last year I implemented from_is_list on the LUV lists.  There were a
> number of complaints from people who don't like the aesthetics of it.
> [...]

It's not simply a matter of aesthetics, but of RFC compliance.
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