Harry Duncan writes:
On Sun, Apr 25, 2010 at 7:56 PM, Dino Ciuffetti <d...@tuxweb.it> wrote:Found the mail header modification that cause DKIM verification probleminmy case from mails coming from gmail.com (and other) to my courier servers. It's "Content-Type" header. Its value is not case protected by the DKIMrelaxed alghoritm specification at sign level, even if CT value should betrated as case insensitive.Sam, since changing/fixing the DKIM canonicalization standard is not a simple thing and will probably require a long time, is it possibile / may have sense / would you have time and desire to write a work around in courier to leave the CT value as it comes from the remote smtp client if it is not broken (avoid changing ISO-8859-1 to iso-8859-1)?If memory serves me right this problem crops up with Courier MLM modifying a message when it is being redistributed. In that case, shouldn't the solution be that CourierMLM resigns the message as the origin of the distributed message? Other than that to my mind, you are going to end up chasing a never ending list of exceptions where something gets changed and DKIM breaks, and sticking plaster after sticking plaster to keep it working.
couriermlm does not alter the message except for adding and/or optionally removing some headers, as described in the man page. In either case, couriermlm does not alter the MIME headers.
Courier itself does not modify the Content-Type header when it rewrites a message, it only modifies Content-Transfer-Encoding. I seem to recall someone else mentioning that the DKIM issue was really tracked down to Gmail rewriting headers, not Courier. In any case, Courier's MIME rewriting can be disabled by setting BOFHBADMIME and MIME, see submit and courier man pages.
If you can put together a standalone test case that seems to indicate that Courier is rewriting headers even when BOFHBADMIME and MIME is set appropriately, then I can look into why this is going on, but I'm fairly certain that these two settings will turn this off completely.
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