Fail to send messages when the receiver's name containing non-ASCII characters

[Hongxu Chen <leftcopy.chx@gmail.com>]

Dear all,

   I am having problems to send messages when the receiver's mail
   containing non-ascii characters. It's not about the address itself,
   but the display name ahead. For instance:

     DISPLAY <mailadress@some.org>

   The `DISPLAY' can be unicode characters other than characters whose
   value is between 0 and 255, but when sending such messages, emacs
   would complain messages like this:

     Assertion failed: (save-excursion (goto-char (point-min)) (not (re-search-forward "[^-ÿ]" nil t)))

  It also WARNS that:

    NUL characters found, which may cause problems.  Continue sending? (d, r, s, e, ?): 

    when the non-ascii character is contained in the mail content(just
  like THIS MAIL).

  And here is my settings for sending messages(just for the reference,
  although I think they have nothing to do with the issue):

  (setq gnus-message-archive-group "nnmaildir+mymailbox:sent")
(setq message-send-mail-function 'smtpmail-send-it
      smtpmail-starttls-credentials '(("smtp.gmail.com" 587 nil nil))
      smtpmail-auth-credentials '(("smtp.gmail.com" 587 "leftcopy.chx@gmail.com" nil))
      smtpmail-default-smtp-server "smtp.gmail.com"
      smtpmail-smtp-server "smtp.gmail.com"
      smtpmail-smtp-service 587
      smtpmail-local-domain "STAP")

  Has anyone else ever encountered similar problems?

Thanks,
Hongxu Chen