Match mail headers case-insensitively when encoding

* lisp/mail/rfc2047.el (rfc2047-encode-message-header): Bind
'case-fold-search' to t when looking up the encoding method,
otherwise a header spelled "CC" is encoded using the wrong
method.  (Bug#77866)

(cherry picked from commit 7d886f214e165d84d3fdbe14b3766d9e88056529)

diff --git a/lisp/mail/rfc2047.el b/lisp/mail/rfc2047.el
index 78a49924b3910f59e0a1f2200046605ebd9354e8..5fc53f1db974ef300462b1eb597a3204e27a2f74 100644 (file)
--- a/lisp/mail/rfc2047.el
+++ b/lisp/mail/rfc2047.el
@@ -265,7 +265,8 @@ Should be called narrowed to the head of the message."
                 (if (= (length charsets) 1)
                     (cons (mm-charset-to-coding-system (car charsets))
                           mm-coding-system-priorities)
-                  mm-coding-system-priorities)))
+                  mm-coding-system-priorities))
+                (case-fold-search t))
            (while (setq elem (pop alist))
              (when (or (and (stringp (car elem))
                             (looking-at (car elem)))