I would reconsider the "Unlimited Emails" offering for the "Ultimate" $100/mo plan. Assuming you're using SES, a customer sending 1,065,000 emails would cost ~$100. All it takes is one person to abuse it before it's costing you big money.

On the surface, "Unlimited" sounds great, but your target market is developers that know the cost of sending emails. This may result in the opposite effect as it signals your model may not be scalable if there's not enough low usage accounts to subsidize the additional costs of sending emails.