Email Design System for Sketch
Targeted.io
Really Good Emails
Stamplia
Mail Designer 365
Stripo
HTMLEmail.io
Paperplane
Mail UI Kit by InVision
Stamplia
Really Good Emails
Pistachio Email Templates
Passport by Mailjet
Templates by Email Monster
MJML
Good Email Copy
Targeted.io - Test your email designs across 30+ clients before you send'm
Stamplia - High converting and beautifully designed email templates
Really Good Emails - A large collection of good product email design.
Pistachio Email Templates - Delicious newsletter templates built for automation
Mail Designer 365 - Discover Mail Designer 365, the easiest way to design mobile-optimized HTML emails, templates and newsletter designs. Your HTML email designer for Mac.
Passport by Mailjet - Create beautiful, responsive e-mails