command to insert a "--text follows this line--"

[Dan Jacobson]

In sendmail.el, in addition to
C-c C-f C-a     mail-mail-reply-to
C-c C-f C-b     mail-bcc
C-c C-f C-c     mail-cc ...
there ought to be a
C-c C-f C-l     mail-separator
which will insert a "--text follows this line--" line,
for folks who have done M-x mail-mode on a buffer, and are inserting
the components into that buffer one by one. (That buffer was already
pretty much a mail message, or else one would have done C-x m).
Hmmm, in gnus this could be called message-insert-delimiter.