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[dkim-ops] Automated System sending "unverifiable" mail

2009-09-11 15:02:12
Hi everyone,

I hope this isn't off-topic.  I'm happy to share what I have on the list or
off if anyone can give me a hand...

We are running a network consisting of MS Exchange internally, with an
outgoing gateway with Postfix 2.3.3 and dkim-milter 2.8.3.

Life has been good for three months or so.  However, I've gotten complaints
from some of our end-users that mail is being bounced back to them.  I took
steps to diagnose the problem by sending mail to the two DKIM verification
systems that I've used to ensure our keys/mail/DNS is good (at sendmail.organd
port25.com), and all of our mail is good as far as these are concerned.

So I kept digging.

We use a package called RT, or "Request Tracker" to service our customers'
requests.  It turns out that email being generated from RT cannot (according
to the port25 service) be verified.  Now, I've generated mail on that host
myself with a script writing to localhost:25 a stream that is apparently
fairly similar to RTs.  All mail goes from postfix to Exchange then to
postfix (dkim-milter) and then to the recipient's MX host.  One of our
customers is rejecting the mail, and apparently for good reason.

I'm trying to figure out how to debug this.  We've seen zero issues with
this so far, and my spoofing mail from that same host doesn't trigger this
problem, but this application (mostly Perl) seems to be formatting mail in
such a way as that the milter generates an invalid signature.

I'm going to look at the 7-bit v. 8-bit coding, the specifics of things line
newlines generated by this system, etc., but if anyone has any other ideas
I'd really appreciate it.  And it actually is kind of interesting... I
think.

And, I apologize if this is wrongly-directed.  Thanks in advance.

_KMP
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