When debugging a DKIM signature failure, I found that:
* Thunderbird doesn't care at all about the SMTP line length limit, happily sending longer lines
when you quote a 1000-charachter line,
* Postfix happily accepts the too-long-line, passing it as-is to opendkim
* opendkim is unmaintained and doesn't care either, signing the too-long line,
* Postfix (and other MTAs downstream too, probably) will truncate the line as documented, breaking
the DKIM signature.
Obviously the Real (tm) bug(s) here are in Thunderbird and, arguably, opedkim, but I am left
wondering whether line_length_limit should apply in this case (and if it should not, too, be 1000,
or 998, characters by default). The, fairly vague, docs say only
"Upon input, long lines are chopped up into pieces of at most this length; upon delivery, long lines
are reconstructed."
which doesn't tell me when they are chopped up into pieces, or how that is done (presumably the same
pattern replacement as smtp_line_length_limit?).
Given opendkim is unmaintained and the world of MUAs is filled with...less than spec-compliant
things, it seems like it would be ideal for there to be some way to work around this at the
Postfix-level without writing a custom milter. Is there any desire to adapt line_length_limit to
apply in this case?
Thanks,
Matt
