Mailtrack is a free email tracker for Gmail that allows users to track when their emails have been read, how many times they have been opened, and the number of clicks. It adds intuitive checkmarks to emails for read receipts and provides access to a dashboard to filter read and unread emails. Mailtrack offers a free and unlimited version with a signature, as well as Pro and Advanced versions with extra features such as link tracking, real-time read receipts, and integration with CRMs. It has over 5 million sign-ups, 100,000 customers, and has been featured in various publications.