sending mail wants to setup mail (again)

[Eli Zaretskii]

Starting with this morning, Emacs that was set up for sending mail
eons ago, and worked flawlessly till now, suddenly wants to be set up
again:

   Emacs has not been set up for sending mail.

   Type `y' to configure and use Emacs as a mail client,
   or `n' to use your system's default mailer.
   
   To change your decision later, customize `send-mail-function'.

For some reason, it now wants an explicit customization of
send-mail-function in my ~/.emacs.  If I don't, send-mail-function is
set to sendmail-query-once.  Unless this is a bug, this "query once"
will no doubt annoy gobs of users out there.