Sidemail - The simplest way to send transactional emails. Sidemail makes sending transactional emails trivial, it's perfect for side projects, MVPs or the next big thing.
HTMLEmail.io - Responsive HTML email templates for startups & developers
Semplates.io - Create, edit and manage all your email templates on AWS SES with ease.
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
Mailook - Identify & fix your email deliverability issues for free 👀
MJML - The open source framework for responsive emails