Really Good Emails - A large collection of good product email design.
Email Marketing: A Beginner's Guide - Master email marketing with these 3 short ebooks from Drip.
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.
HubSpot Free Email Marketing - Powerful drag and drop email marketing in the HubSpot CRM
Email Design System for Sketch - Sketch file with 10 email templates for designers
Quokka (formerly Kryptowire) - The gold standard in SAST, MAST, IAST, and more!