Open Source Android Email Clients

Tutanota is an open source email client focused on security and privacy. It is built with end-to-end encryption and 2FA, so you can be assured of utmost email security. Tutanota is always encrypted, so whether you’re using their secure webmail client, mobile apps or desktop clients, you can be sure to communicate securely.

K-9 Mail is an advanced, open-source email client for Android that's focused on making it easy to chew through large volumes of email. It's designed to be easy to use by both novice and power users, with plenty of useful features. It has IMAP push email support, support for multiple accounts, support for POP3 and Exchange 2003/2007 (with WebDAV), flagging, filing, signatures and more! K-9 Mail also offers a light and dark theme, keyboard shortcuts and emoji support. Like man's best friend, K-9 Mail is an email client you can depend on, and will surely be your best friend when it comes to handling your emails!

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.

GoldBug is a decentralized & secure communication suite that offers an integrated e-mail client, an instant messenger & a file transfer. Also included is an URL-RSS-DB & a p2p web search. Current vers. w/ McEliece Algorithm. GoldBug has been 2013 - 2023 ten years just another Graphical User Interface of the Spot-On Encryption Suite. Main GUI features: Minimal & colorful Interface with Tabs in the East. Microsoft & Qt MinGW deprecated Win32 & for Compiling: ● https://sourceforge.net/p/goldbug/wiki/compiling As Spot-On implemented the minimal GB-concept & Nuvola Icons, GoldBug has now been fully integrated into Spot-On Win64: Just choose Tabs at East & Mini-View in Options - w/ Nuvola Icons of course! Voilá! & Many Thanks, Pro-Files can be found archived at ● current source: https://github.com/textbrowser/spot-on ● EN Manual: https://www.amazon.com/dp/3749435065 ● DE: https://compendio.github.io/goldbug-manual-de/ ● Study: https://www.amazon.com/asin/dp/3750408971

PeerBox is the first fully functional P2P messaging system. Messages travel directly between machines via SSH over Tor Hidden Services. No central server, no intermediary, no account required. Local data is encrypted in AES-256 via gocryptfs with self-destruct after five failed password attempts. Messages are signed and encrypted with GPG. Only explicitly accepted contacts can reach you, making spam structurally impossible. Runs on Debian-based distros with a fully automated installer. Accessible from mobile via the PeerBox Server plugin. Written in Python, published under AGPL on Codeberg.