If the encoding is `qp-or-base64', then either quoted-printable
or base64 will be used, depending on what is more efficient.")
+(defvar mm-use-ultra-safe-encoding nil
+ "If non-nil, use encodings aimed at Procrustean bed survival.
+
+This means that textual parts are encoded as quoted-printable if they
+contain lines longer than 76 characters or starting with \"From \" in
+the body. Non-7bit encodings (8bit, binary) are generally disallowed.
+This is to reduce the probability that a broken MTA or MDA changes the
+message.
+
+This variable should never be set directly, but bound before a call to
+`mml-generate-mime' or similar functions.")
+
(defun mm-insert-rfc822-headers (charset encoding)
"Insert text/plain headers with CHARSET and ENCODING."
(insert "MIME-Version: 1.0\n")
"application/octet-stream"
(mailcap-extension-to-mime (match-string 0 file))))
+(defun mm-safer-encoding (encoding)
+ "Return a safer but similar encoding."
+ (cond
+ ((memq encoding '(7bit 8bit quoted-printable)) 'quoted-printable)
+ ;; The remaing encodings are binary and base64 (and perhaps some
+ ;; non-standard ones), which are both turned into base64.
+ (t 'base64)))
+
(defun mm-encode-content-transfer-encoding (encoding &optional type)
(cond
((eq encoding 'quoted-printable)
(while rules
(when (string-match (caar rules) type)
(throw 'found
- (if (eq (cadar rules) 'qp-or-base64)
- (mm-qp-or-base64)
- (cadar rules))))
+ (let ((encoding
+ (if (eq (cadar rules) 'qp-or-base64)
+ (mm-qp-or-base64)
+ (cadar rules))))
+ (if mm-use-ultra-safe-encoding
+ (mm-safer-encoding encoding)
+ encoding))))
(pop rules)))))
(defun mm-qp-or-base64 ()