Serial Mail and pppd

Hi all,

I have installed qmail on rh7.3. It runs fine. 

I am also running pppd with the "demand" option. This is to connect for
other purposes. I want qmail to accept messages from a local network,
but not to send them, and then schedule a connection at regular
intervals. Only once the connection comes up, do I want to messages in
the queue to be sent.

At the moment, what is happening is that as soon as a message enters the
queue, it triggers the dial-on-demand in pppd and gets sent straight
away. (not sure if this is trigger by actually trying to send the
messages, or by doing the mx lookup...).

Is there any way I can configure serialmail/qmail to not even try and
send messages. I have read how-to's on configuring serialmail, but they
do not cover using the dial-on-demand option with pppd.