It is an email marketing service provider with over 100,000 small business clients world wide. It helps people keep in touch with the subscribers who have requested to be on their mailing list.
Twilio SendGrid's cloud-based email infrastructure relieves businesses of the cost and complexity of maintaining custom email systems. Twilio SendGrid provides reliable delivery, scalability & real-time analytics along with flexible API's.
Amazon SES eliminates the complexity and expense of building an in-house email solution or licensing, installing, and operating a third-party email service. The service integrates with other AWS services, making it easy to send emails from applications being hosted on services such as Amazon EC2.
Mailgun is a set of powerful APIs that allow you to send, receive, track and store email effortlessly.
Mandrill is a new way for apps to send transactional email. It runs on the delivery infrastructure that powers MailChimp.