Free and open source webmail software
SquirrelMail is a PHP-based Web email client. It includes built-in pure PHP support for IMAP and SMTP, and renders all pages in pure HTML 4.0 for maximum compatibility across browsers. It has strong MIME support and a flexible plugin system.
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. This version of Hastymail is no longer being developed. We are now working on a new version, Hastymail 3, AKA, "Cypht". http://cypht.org
NOCC is a simple and fast Webmail client which can handle POP3, SMTP, and IMAP servers. It is written with PHP5 (uses sessions), has low requirements (no database, frames). Features multi-language support, MIME attachments, displays HTML messages.
Columba is an email client written in Java, featuring a user-friendly graphical interface with wizards and internalionalization support. Its a powerful mail management tool with features to enhance your productivity and communication.
EGroupware has moved to Github, please find all our downloads there: https://github.com/EGroupware/egroupware/releases EGroupware is a multi-user, web-based groupware suite. Currently available modules include: email, addressbook, calendar, infolog (notes, to-do's, phone calls), content management, wiki, project management, tracker, timesheet, knowledge base, CalDAV/CardDAV
Business webmail modular application with mobile client
The most complete Business Webmail with Mobile client application for companies of all sizes. All the core functions for business like calendaring and integrated webmail, plus the capability of converting emails into business objects such as: quotes, invoices, marketing stuff, customer requests, project management and more. A simple way to have a unique flow of information from email request from customers to invoices! You only have to choose which modules you want to activate and is done! Built with PHP, loves MySQL but runs also on SQL Server and Oracle.
"Archive This" is an add-on for the Thunderbird email client that provides shortcuts for filing messages into folders rapidly and efficiently.
NOTICE: Keep in mind that POP3ye is alpha software and by definition it is a long way from finished. POP3ye is a fully featured web-based e-mail client written in Object Oriented PHP 5. It ony supports the POP3 protocol.