(mail-citation-prefix-regexp): New variable.

(mail-fill-yanked-message): Pass mail-citation-prefix-regexp
to fill-individual-paragraphs.

lisp/mail/sendmail.el

@@ -173,6 +173,15 @@ instead of no action."
   :type 'hook
   :group 'sendmail)
 
+(defcustom mail-citation-prefix-regexp "[ \t]*[-a-z0-9A-Z]*>+[ \t]*\\|[ \t]*"
+  "*Regular expression to match a citation prefix plus whitespace.
+It should match whatever sort of citation prefixes you want to handle,
+with whitespace before and after; it should also match just whitespace.
+The default value matches citations like `foo-bar>' plus whitespace."
+  :type 'regexp
+  :group 'sendmail
+  :version "20.3")
+
 (defvar mail-abbrevs-loaded nil)
 (defvar mail-mode-map nil)
 
@@ -1124,7 +1133,7 @@ Numeric argument means justify as well."
     (fill-individual-paragraphs (point)
 				(point-max)
 				justifyp
-				t)))
+				mail-citation-prefix-regexp)))
 
 (defun mail-indent-citation ()
   "Modify text just inserted from a message to be cited.