Edit, removed my previous message as it sounded quite negative, wasn't well thought out and was also partially off-topic. Product looks nice and simple, good job!
Email isn't terribly expensive to send--a common rate is roughly $0.80/1,000 emails. It's absolutely dirt cheap ($0.10/1,000 emails) if you can get past the application for AWS SES. (I didn't--don't know the magic words I guess!--so I'm a happy Postmark user instead.)
