MJML - The open source framework for responsive emails
Warmup Inbox - Warmup Inbox is a tool that automates the process of warming up your email inboxes, raising your sender reputation and inbox health automatically.
HTMLEmail.io - Responsive HTML email templates for startups & developers
MailReach.co - The #1 email warming service to improve your deliverability by generating realistic and meaningful engagement to your emails. Easy-to-use solution to help you land in the main inbox instead of the spam folder.
Skymail - Send email via static forms w/ Gmail or other mail services
Warmbox.ai - Warm up your cold email inbox, and never land in spam anymore!