Open Source Mobile Operating Systems Email Clients

Thunderbird iOS is the official iPhone and iPad email client offering from the Thunderbird project, bringing the capabilities of a feature-rich, open-source email experience to iOS devices with native UI and Apple platform integrations. The app gives users a powerful tool for managing multiple email accounts, including IMAP and POP3 configurations, and supports modern authentication flows like OAuth for popular providers. Designed with mobile usability in mind, it includes familiar gestures, thread views, swipe actions, attachment previews, and integrated search so users can stay productive on the go. It also handles common email needs like organizing with folders, setting flags, and filtering messages, while respecting platform norms for notifications, background fetch, and data usage. By maintaining a connection to the desktop Thunderbird project’s ethos, the iOS client places emphasis on transparency, extensibility, and user control.

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.

Trojitá, a Qt IMAP e-mail client

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

Aegis Implicit Mail is a free and open source library which is designed to provide fast and developer friendly API to send emails using SMTP ports. Binaries are available in the form of NuGet package: https://www.nuget.org/packages/AIM Please check http://pki.tools/aim.html as well AIM Supports : * None Ssl Mails * Implicit Ssl Mails * Explicit Ssl Mails * Smtp Connection test * Detect Ssl type of mail server * Attachments for MIME and S/MIME message. * In-line attachment and separate file attachment * All content types and mimes * SMIME , Signed and Encrypted mails In an integrated way Sadly, Microsoft.Net.Mail Ssl Mails does not support Implicit Ssl Mail and it is still used by many servers, including port 465 of Gmail here AIM comes to make a readable and fast alternative to send your smtp mails. For unicode issues please refer to https://sourceforge.net/p/netimplicitssl/tickets/4/ . We really appriciate any help in testing of different encodings

Extensible web mail client, allowing UI to be redefined according target format (modern Web browser, mobile device ...).

LogicMail is a standalone E-Mail client designed to run on RIM BlackBerry handheld devices, providing full support for IMAP, POP, and SMTP over the device's Internet connection. Its exists to provide an alternative to the service-oriented "push" E

Our goal is to implement a sophisticated email client application for mobile devices that supports Symbian under series 60 platform.

An email program to run on micromachines such as pdas'. Java enabled machines are the target audience for this program. Connectivity using bluetooth and infra red using the pda subsystem is also intended .

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.

Proton Mail for iOS is the official iPhone and iPad client that brings Proton’s secure, end-to-end encrypted email service to Apple’s mobile ecosystem, combining strong privacy protections with native performance and gestures. The app allows users to sign in to one or multiple Proton Mail accounts, read and compose encrypted messages, schedule emails, protect emails with passwords, set expiration timers, and organize mail with labels and folders inside a smooth, intuitive iOS interface. It makes use of Apple’s networking APIs and encryption frameworks to deliver seamless management of encrypted communications while respecting platform conventions like touch navigation, Apple notifications, and background refresh. All sensitive operations — including key handling and encryption — occur locally on the user’s device, ensuring that plaintext messages and secret keys are never exposed to Proton’s servers or third parties.

Free Java Office suite on the Web.