This has been my experience as well. At a certain scale, it's worth internalizing this effort of course, but that is (in my opinion) an enterprise-level problem

This has been my experience as well. At a certain scale, it's worth internalizing this effort of course, but that is (in my opinion) an enterprise-level problem (and has an accompanying enterprise-level headache). I've had great experiences with MailGun, Sendgrid and Mandrill. Amazon SES not so much; very cheap but deliverability seems to be an issue (anecdotally).