If you're going to send out that many emails, you probably want some rotational IP software, so that you don't get blocked everywhere.
This can costs upwards of $2000, but it is well worth it.
Plus you'll want to buy a bunch of IP's from your host so that you can rotate between them.
Mine runs on Postfix, and it works well with LMP, although it does add a lot of overhead with the rotating.
I could probably send out about 800k per day, with my Dual AMD Opteron with two gigs ram. With the rotating IP overhead.