Crow.app - Pricing and experimentation tools for Stripe
Amazon SES - Scale your business email & marketing messages with Amazon Simple Email Service (SES), a cost-effective and reliable cloud email service. Sign up today.
Mailgun - A set of powerful APIs that enable you to send, receive and track email from your app effortlessly whether you use Python, Ruby, PHP, C#, Node.js or Java.
MailChimp - MailChimp is the best way to design, send, and share email newsletters.
Stripe for Gmail - Display customers Stripe information within inbound emails
Constant Contact - Constant Contact offers email marketing, social media marketing, online survey, event marketing, digital storefronts, and local deals tools.