One the reasons I know about and use mandrill is that my framework's documentation had 3-5 quick install options and I really picked mandrill at random. This is a bit also like how stripe operates. It's free or dirt cheap to prototype indefinitely. Making sure popular frameworks have first class support (or at least obvious, easy to use installation instructions, and or great API with great documentation) could be a lot of benefit. The UI's inside those applications allow my support and non-dev technician staff to review data, refund payments, resend emails etc. without me having to build them an interface to use.