Ensure that `mail-send' breaks too-long lines

* lisp/mail/sendmail.el (mail-send): Ensure that we fold too-long
lines when using `sendmail-user-agent' (bug#53412).

1 files changed, 4 insertions, 1 deletions

diff --git a/lisp/mail/sendmail.el b/lisp/mail/sendmail.el
index 76c3baf4727..0d3eeecd8c8 100644
--- a/lisp/mail/sendmail.el
+++ b/lisp/mail/sendmail.el
@@ -955,7 +955,10 @@ the user from the mailer."
               (error "Invalid header line (maybe a continuation line lacks initial whitespace)"))
             (forward-line 1)))
         (goto-char opoint)
-        (when mail-encode-mml
+        (when (or mail-encode-mml
+                  ;; When we have long lines, we have to MIME encode
+                  ;; to get line folding.
+                  (mm-long-lines-p 1000))
           (mml-to-mime)
           (setq mail-encode-mml nil))
         (run-hooks 'mail-send-hook)