K-9 Mail is an open source email client with support for multiple accounts, search, IMAP push email, multi-folder sync, flagging, filing, signatures. Developed by K-9 Dog Walkers
License: Open Source
K-9 Mail is a highly customizable, open-source email client focused on Android users, while Nylas Mail offers a modern, cross-platform experience with integrated calendar and contact features, making it suitable for users who need a comprehensive email solution.