Stackmails and Mailshake are two tools used for email outreach. Stackmails is an automated email outreach tool that offers a wide range of powerful features to help users reach out to customers, influencers, and leads. It offers personalization options, automated follow up emails, email tracking, and automated scheduling. On the other hand, Mailshake is an email outreach tool that focuses on simplifying the process of sending newsletters and personal emails. It has an easy-to-use automated contact management system and CRM that allows users to quickly identify leads and create personalized templates. Stackmails is more feature-rich, while Mailshake is easier to use and has fewer features. The main difference between the two is that Stackmails offers more options in terms of automation and tracking, while Mailshake does not.