RoundCube Webmail is a PHP webmail client that will work with a MySQL or Postgres database. One appealing feature it brings is the ability to skin the application-style user interface using XHTML and CSS 2. The app is a multi-language IMAP client whose features include MIME support, address book, editable folder search and spelling check, and it works in your web browser too.

Horde is more just a mail client, it is an enterprise-focused groupware. Horde is capable to read, send and organize mail correspondence, fully manage contacts, calendars, tasks and various notes. Horde is using its own PHP framework with libraries to insure possibility of building custom solutions.

Zimbra also works in web browsers. But it isn’t like PHP web clients as it uses the AJAX set of web technologies instead. It offers email and calendar functionality and you can view messages and conversation formats. Its approach to visual search is particularly effective in making short work of managing the largest inboxes. Zimbra is one of the open-source webmail clients and it will accept third-party add-on apps so you can view things like maps (for example) without having to navigate away from the message you’re currently looking at.

Xuheki makes use of a fast browser-based AJAX client and the IMAP protocol for go-anywhere message access. It’s a well-featured solution and it’s also worth mentioning that Buheki is released under the GNU General Public License.

AtMail is a free Ajax Webmail client that allows users to access their messages via web browsers and WAP devices. You can install it on Windows and Linux systems and it supports IMAP/POP3 mailboxes. It’s got an optional email-server mode that uses Exim as the MTA.

AfterLogic WebMail Lite PHP works with PHP 4.1 and above. It’s a webmail script with a very contemporary look that works with AJAX and supports skins. It works with POP3 and SMTP, so it can integrate with web browsers, and it comes with all the usual functionality you would expect, such as the ability to add lots of attachments, multiple mail accounts, and domains. It has a preview panel, and administration is via the web. It’s easy to get up and running, and it’s also open source. Perhaps the best aspect of all is that it’s free. You’ll only need to pay if you want to take advantage of any of the features that come with the better-specced professional version.

Another one of the PHP webmail clients in our list is Hastymail, a fully-featured IMAP/SMTP solution that works with tablets, phones, text browsers, and run-of-the-mill web browsers. Hastymail’s architecture lets PHP developers adapt its functionality with plugins and these add-on apps let you add extra pages (along with any required CSS files), insert XHTML to make changes to pages, alter internal data structures inside Hastymail, make AJAX callbacks with its AJAX system, and have it converse happily with a configured SQL server.

Mailr is not one of the PHP webmail clients on our list, running instead on Ruby, which sits on top of the Ruby on Rails web app framework. It’s been tested on Courier-IMAP but should also be perfectly au fait with other IMAP servers too.

This app is based on Ajax and it features webmail, address book, and note-taking functionality. The calendar and web disk features have yet to be finalized but the instant messenger and RSS reader are up and running at the time of writing. Protection comes as standard and it’s the first open-source web app to feature it. It also offers Web 2.0 technologies and was created using Java. It makes use of JSP/Servlets and J2EE technologies and requires MySQL database to do its thing.

Postaci is built with PHP and is a POP3/IMAP email client that was designed to be a cinch to use. It supports SMTP authentication and can manage both protocols. If you want to change the default program you can do that using just one configuration file. Postaci works with any platform, and with any operating system that can handle PHP. It does not depend on one particular database so it can be used with MySQL, mSQL, Microsoft SQL, Sybase, and PostgreSQL.