Right now we're not doing anything special. We just send the emails from the server as we need to. A lot of the emails are set up as nightly jobs which we queue up in a DB before we send.
I asked because I'm the Product Manager of PostageApp, and we specialize on those sorts of emails. Let me know if you'd be interested in giving our app a whirl, it takes the headaches of deliverability out of your hair. :)