The Postmark team is absolutely awesome. Forrst has been a happy customer since very early on, and Chris and team have gone out of their way to be helpful wherever possible. It's a huge reason why we haven't even considered Amazon or anyone else.
I second this. We've been sending out daily e-mail reports with PDF attachments to our customers and their API is easy to setup, easy to use and even makes attachments simple. To me, they've picked one thing and they're owning it.
I've done quite a few interviews in my career, and Paul's top notch. Big thanks to him for his care for the industry, and producing a high quality blog in a sea of crap. :)
I use Postmark at my app and it works really well! Support is good and you know you will be talking to real people that cares. I have no idea how Amazon support works, but I guess that Postmark can do it better.
Ever heard of notice of receipt? Built into public mail clients since like ever.