I use Postmark for any kind of transactional email in production, since I can't use them for mailing lists, I use Mailchimp. I recently tried Amazon SES which is still in beta, but it's very easy to use and cheap. But I can't compair it at all with Postmark. The kind of support I get from those guys over at Wildbit is great, something you will probably never experience on AWS. It is definitely a time sink to setup and manage all the right requirements for an almost perfect email solution. I just directly save all those hours and headaches and delegate that to the guys who know about that and do it right.