Roundcube Webmail - Browser-based multilingual IMAP client

•    PHP

Roundcube Webmail is a browser-based multilingual IMAP client with an application-like user interface. It provides full functionality you expect from an email client, including MIME support, address book, folder management, message searching and spell checking.

Hastymail - IMAP/SMTP client in PHP

•    PHP

Hastymail is a fast, secure, rfc-compliant, cross-platform IMAP/SMTP client application written in PHP providing a clean web interface for sending and reading E-mail. It is compatible with PDAs, phones, text browsers, and all mainstream browsers. The ability to use a database for storing user settings, contacts, and plugin data, with support for both Postgresql and Mysql.

Mailspring - A beautiful, fast Webmail

•    Javascript

Mailspring is built on the modern web with Electron, React, and Flux. It is designed to be extensible, so it's easy to create new experiences and workflows around email.

Cypht - Lightweight Open Source webmail written in PHP and JavaScript

•    PHP

All your E-mail, from all your accounts, in one place. Cypht is not your father's webmail. Unless you are one of my daughters, in which case it is your father's webmail. Cypht is like a news reader, but for E-mail. Cypht does not replace your existing accounts - it combines them into one. And it's also a news reader..

Rainloop Webmail - Simple, modern & fast web-based email client

•    PHP

Simple, modern & fast web-based email client.Modest system requirements, decent performance, simple installation and upgrade, no database required - all these make RainLoop Webmail a perfect choice for your email solution.

Mailpile - Mordern Web Mail

•    Python

Mailpile is a modern web-mail you run on your own computer. It is a personal e-mail searching and indexing tool, largely inspired by Google's popular proprietary-but-gratis e-mail service. It wants to eventually become a fast and flexible back-end for awesome personal mail clients, including webmail. It supports importing archived mails from Gmail, IMAP server, Mbox etc. It supports PGP encryption and verification of emails and recipients.

SharpWebMail - ASP.NET Webmail Application

•    CSharp

SharpWebMail is an ASP.NET webmail application that is written in C#. It uses a POP3 or IMAP servers as the mailstore and sends mail through a SMTP server. It is very simple to configure (only a few settings in the web.config file). You can compose HTML messages, search your inbox, read complex mime messages, have multiple address books and much more.

Modoboa - Mail hosting made simple

•    Python

Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface. It provides useful components such as an administration panel or a webmail. Its main features include Administration panel, Amavisd-new frontend, Webmail, Per-user Sieve filters, Autoreply messages for Postfix, Graphical statistics about email traffic and lot more.

ProtonMail - Web client for the ProtonMail secure email service

•    Javascript

ProtonMail provides secure email service. All emails are secured automatically with end-to-end encryption. This means even we cannot decrypt and read your emails. As a result, your encrypted emails cannot be shared with third parties.

Tutanota - Encrypted MailBox

•    Javascript

Tutanota automatically encrypts all your data on your device. Your emails as well as your contacts stay private. You can easily communicate with any of your friends end-to-end encrypted. Even subject and attachments as well as all your contacts are encrypted. It provides an open webmail service that is very easy to use.

Nwebmail

•    C

Nwebmail is a webmail client written in ANSI C. It allows users to check and send email from any web-browser. It accesses the mail spools directly for fast and efficient mail processing. It supports MIME attachments and can import/export address books.

sync-engine - :incoming_envelope: IMAP/SMTP sync system with modern APIs

•    Python

The Nylas Sync Engine provides a RESTful API on top of a powerful email sync platform, making it easy to build apps on top of email. See the full API documentation for more details.Install the latest versions of VirtualBox and Install Vagrant.

Opo Perspective

•    DotNet

Opo Perspective is a webmail client developed with ASP.NET MVC and C#. - Flexible (different mail servers and protocols) - Extensible (add functionality like calendar, notes etc. as modules) - Ajaxified UI (unobtrusive JavaScript using jQuery) - Conversations, tags, search etc.

Claws Mail - Email Client and News Reader Based on GTK+

•    C

Claws Mail is a GTK+ based, lightweight, and fast e-mail client and newsreader. Supports POP3, APOP, IMAP, SMTP, SMTP AUTH, NNTP, LDAP, multiple accounts, spell-checking, addressbook, SSL, GPG, filtering, i18n, & more. It is further extended by plugins. Lots of extra functionality, like an RSS aggregator, calendar, or laptop LED handling, are provided by extra plugins.

Qmail POP-toaster setup guide

This is a documentation project that is useful for people who are looking to set up an e-mail system with an easy-to-use client webmail front end and support for name-based virtual domains. It proposes a Qmail-Vmailmgr-Courier-SquirrelMail tie-in as the b

nylas-mail - :love_letter: An extensible desktop mail app built on the modern web. Forks welcome!

•    Javascript

Nylas Mail is an open-source mail client built on the modern web with Electron, React, and Flux. It was designed to be easy to extend, and many third-party plugins are available that add functionality to the client.⚠️ Nylas Mail was initially released and open-sourced in early 2015 and was maintained by Nylas until Spring 2017. While Nylas no longer supports Nylas Mail, you can download the latest release or build it from source. There are also several forks that are being actively developed and maintained.

Citadel

•    C

Citadel is a collaboration suite (messaging and groupware). It provides support for Email, Calendaring/Scheduling, Address books, Bulletin boards, Mailing List Server, Instant Messaging, Wiki, Multiple domain support.

W3MAIL - Web Mail

•    PHP

W3MAIL - fast and small webmail client written in PHP5. It provides easy webmail access to IMAP accounts and has very few requirements to install. Features multi-language support, simple contacts manager, MIME attachments, displays HTML messages.

Sylpheed - Lightweight and user-friendly e-mail client

•    GTK

Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client. It provides intuitive user-interface, Powerful filtering and search, Junk mail control, Security features (GnuPG, SSL/TLSv1). Sylpheed supports not only the major protocols such as POP3, IMAP4rev1 and SMTP, but also NNTP (NetNews). IPv6, which is the next-generation Internet protocol, is also supported by default.

K-9 Mail – Advanced Email for Android

•    Java

K-9 Mail is an open-source email client for Android.