Earlier quoted context omitted.
These are not really comparable products. MailChimp is an email broadcast and subscription management service. It's for sending things like email newsletters and marketing campaigns. SES/Postmark/Sendgrid are more for one-to-one type communications, e.g. delivering your application's forgot password email.
Ah, thanks for that clarification. However, I would have thought that the "one-to-one type communications" would be more expensive (per email), than sending to lists. Amazon seems to allow both, at a much lower cost.
* Until today, MailChimp was by far the cheapest option, esp. if you compare them against similar services, e.g. Campaign Monitor.
* Mailchimp is a lot more than a dumb email server...it's a list management service, it offers stats, a pretty robust API, etc. You'd have to spend a lot of time to build up those capabilities around SES.
* I'm not sure SES is meant to handle the volume MailChimp handles. (I don't mean technically, I more mean what is allowed by Amazon.)
Just a few thoughts from a pretty well satisfied MailChimp customer. (I'm also a SendGrid customer, and you can bet I'll be taking a close look at SES as a replacement for that service.)