GrowthList - A crowd-sourced list of growth hacks
Email Marketing: A Beginner's Guide - Master email marketing with these 3 short ebooks from Drip.
Q by SubStrata - Q is your email communication genius for B2B sales.
HubSpot Free Email Marketing - Powerful drag and drop email marketing in the HubSpot CRM
Quokka (formerly Kryptowire) - The gold standard in SAST, MAST, IAST, and more!
EmailOctopus - Email marketing for less, via Amazon SES