Before 2012 (when they launched Mandrill) MailChimp used Amazon SES. http://us1.campaign-archive1.com/?u=f7b9ee22124ff6454424dc10...
The Mandrill service is nice, I agree.
Also, MailChimp has a very cool 404 page: http://kb.mailchimp.com/article/transactional-reports-overvi...
(First used MailChimp in 2003 and they've always been the bomb.)