Really Good Emails - A large collection of good product email design.
GrowthHackingIdea.com - One short, curated growth hacking idea a day to your email
Good Sales Emails - Best sales emails from great companies
Growth Hacking Sourcebook - The ultimate growth hacking sourcebook
Great Email Copy - A dose of emails from around the web.
Email Growth Playbook - Increase your email ROI with 60+ growth tactics