[Exim] Large email lists and performance

I have an email list of 30,000 names. Sendmail gets the list out in
about 6 hours (using linuxconf vdeliver). I;m looking for a way to do
the same thing with exim. What I want is for exim to treat them as
30,000 individual messages.

So far - with a list of just 250 addresses it takes about 20 minutes for
exim to start sending - although it only takes a couple of minutes once
it starts. I don't understand the sending delay.

Anyone got and tips on this?