problem with sendmail-send-it

[Hikaru Ichijyo]

I can successfully post to Usenet, but when I try to send email in Gnus,
I get:  "Symbol's function definition is void: sendmail-send-it"

Is there a problem with using sendmail-send-it in Gnus?  I did use VM
for awhile, and it worked there, though I didn't like VM otherwise.  The
reason I'd prefer it is because I have a local network setup, and
Postfix knows whether you send mail out to the ISP or keep it on my LAN.
Since the Postfix service is on the same machine, it'd be silly if I had
to resort to SMTP to inject mail into it.

Here is an edited down excerpt of some of my ~/.emacs:

(setq mail-user-agent 'message-user-agent
      read-mail-command 'gnus
      send-mail-function 'sendmail-send-it
      message-send-mail-function 'sendmail-send-it
)

-- 
He that would make his own liberty secure must guard even his enemy from
oppression; for if he violates this duty, he establishes a precedent
that will reach to himself.
                                        --Thomas Paine