Spent over 1 year cruising through their free credits, now happily paying a couple hundred a month without a second thought.

It's really intuitive and easy-to-use to see errors, read text of emails, and so forth.

Side note: It's neat to see people come out of the woodwork on this thread for Postmark, which is normally one of those products consumed so quietly, and under-appreciated. I bet their team is really happy to see this. :)