INSTAD.IO - Automagically converts vector images into sketchy style
Really Good Emails - A large collection of good product email design.
Base UI Sketch Framework - Huge set of everything you need to design and prototype
Stripo - Stripo is an all-in-one email design platform. We enable our clients to build emails of any complexity, including interactive AMP emails, really fast and easy.
Sketch Extensions - An official collection of Sketch extensions & plugins
Email Love - Email design inspiration, templates and discovery