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Sendmail 8.14.4 and tabs in long headers

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  Sendmail 8.14.4 and tabs in long headers om@iki.fi (Otto J. Makela) - 2026-10-22 20:50 +0300
    Re: Sendmail 8.14.4 and tabs in long headers Claus Aßmann <INVALID_NO_CC_REMOVE_IF_YOU_DO_NOT_POST_ml+sendmail(-no-copies-please)@esmtp.org> - 2026-10-23 01:54 -0400

#8372 — Sendmail 8.14.4 and tabs in long headers

I am forced (due to circumstances which I cannot currently rectify)
to run Sendmail 8.14.4 on a system where it cannot be updated.

It turns out this version rewrites tabs in long multi-line headers
(like To or Subject) into spaces. This unfortunately breaks DKIM
signatures using c=simple, and then of course messages bounce if
the From domain specifies p=reject in their DMARC.

Newer Sendmail versions do not of course do this. I've tried to look at
the ruleset, but haven't been successful in locating where this happens.
Anyone remember what part of it causes this rather unfortunate rewrite,
or was this part in the actual compiled source code?
-- 
   /* * * Otto J. Makela <om@iki.fi> * * * * * * * * * */
  /* Phone: +358 40 765 5772, ICBM: N 60 10' E 24 55' */
 /* Mail: Mechelininkatu 26 B 27,  FI-00100 Helsinki */
/* * * Computers Rule 01001111 01001011 * * * * * * */

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#8373

Otto J. Makela wrote:

> It turns out this version rewrites tabs in long multi-line headers
> (like To or Subject) into spaces. This unfortunately breaks DKIM
[[...]]

> Newer Sendmail versions do not of course do this. I've tried to look at
[[...]]
> Anyone remember what part of it causes this rather unfortunate rewrite,
> or was this part in the actual compiled source code?

It's not done in the rules - so if there was any change in the
behaviour it's in the code (the release notes don't mention it).

Good luck finding that :-(

-- 
Note: please read the netiquette before posting. I will almost never
reply to top-postings which include a full copy of the previous
article(s) at the end because it's annoying, shows that the poster
is too lazy to trim his article, and it's wasting the time of all readers.

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