Re: DKIM, Sendmail and Feature(`nocanonify') - Was Re: SA DKIM related bug 6462 - Possibly Gmail, Sendmail and/or Thunderbird related?

From: Murray S. Kucherawy <msk_at_blackops.org>
Date: Fri, 16 Dec 2011 10:41:00 -0800 (PST)

I should add that you seem to assert that what sendmail does is copy the
envelope sender to the To: field, which is not what's happening. The
description of the "nocanonify" feature says:

"Don't pass addresses to $[ ... $] for canonification by default, i.e.,
host/domain names are considered canonical, except for unqualified names,
which must not be used in this mode (violation of the standard)."

"$[ ... $]" is sendmail.cf language for hostname resolution. So what it's
really doing is taking "PCCC.COM" and asking the resolver to come back
with a canonical name for it, and using that instead. Thus, presumably
sendmail's resolver routines (which are based at least in part on the DNS
resolver and maybe an /etc/hosts check, since this code goes back a long
way) are deciding that the canonical form of PCCC.COM is pccc.com, and
replacing the string accordingly. What's in the envelope isn't really
used here, and certainly DKIM has no idea what's in the envelope.

I haven't looked at the sendmail source code recently (I haven't worked
there in a few years), but the above rings fairly true to what I recall.

-MSK
Received on Fri Dec 16 2011 - 18:41:16 PST