Open Source Kotlin Email Clients

Thunderbird Android is the mobile counterpart of the popular Thunderbird email client, reimagined for Android phones and tablets so users can access, send, and organize email from multiple accounts with advanced features found in desktop clients. It embraces modern mobile UI design while supporting robust email protocols (IMAP/POP3) and standards like OAuth for secure logins to services such as Gmail, Outlook, or custom mail providers. The app is built to handle complex mailbox structures, threaded discussions, rich text and HTML content, attachments, and account synchronizations reliably even on cellular connections. With features like unified inboxes, background fetch, push notifications, and configurable swipe actions, Thunderbird Android aims to bring the power and flexibility of the desktop experience to your pocket. It also integrates search, filtering, and tagging capabilities that help users stay organized when managing large volumes of mail.

Proton Mail for Android is the official mobile application that lets users access their Proton Mail encrypted email accounts securely on Android devices, providing the full suite of messaging features while preserving end-to-end encryption and user privacy. Designed for modern Android phones and tablets, the app lets users send, receive, organize, and search encrypted emails, create new Proton accounts, manage multiple accounts, and apply labels or folders to keep messages tidy — all within a responsive, touch-optimized interface. It supports composing messages, viewing attachments, handling contacts, and configuring account and mail settings from within the app, giving users portable access to their secure inbox wherever they go. Because ProtonMail’s service never sees unencrypted content, the Android client performs necessary encryption and decryption on the device, aligning with Proton’s privacy-first philosophy and open-source security model.