bug#53412: 27.1; sendmail does not wrap overlong lines

[Francesco Potortì]

I use sendmail-user-agent (rather than message-user-agent) to send
email.  I have mml-mode in the mail-mode-hook.  When I have overlong
lines (> 1000 characters) Emacs should wrap them, as they are not
allowed in SMTP.  This should be standard behaviour, but it is not.

Digging in the source, I found mm-use-ultra-safe-encoding, which should
do that (among other things).  By the way, its doc string says that long
lines are wrapped to prevent broken email servers from breaking; that's
inaccurate: overlong lines are prohibited.

However I tried to set it, mm-use-ultra-safe-encoding is ignored, I have
not understood how it should be set.  I worked around it by

(add-hook 'mail-send-hook
          (lambda () (and (mm-long-lines-p 1000)
                          (mml-to-mime)))) ; break overlong lines

but breaking overlong lines should be the normal behaviour, not a user
option to be explicitly activated.




In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2021-11-27, modified by Debian built on x86-csail-01
Windowing system distributor 'The X.Org Foundation', version 11.0.12014000
System Description: Debian GNU/Linux bookworm/sid

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Configured features:
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LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF XFT ZLIB
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Important settings:
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