Ask HN: Best way to send out large-scale emailers?

A friend of mine has been running a fairly successful e-commerce operation for the last 3 years, and he's been having trouble with sending emails to a mailing list of between 700 and 800k email addresses. Basically, the volume of emails is starting to bog down his servers and T1 lines. Does anyone have suggestions for 1) balancing he load when sending the emailers out to minimize the impedance of email campaigns on the servers and connection or 2) a cost-effective alternative to which the email campaigns can be outsourced.

Thanks!