MailBee WebMail Pro PHP is advanced but easy-to-install web-based email client with modern AJAX interface. It's built as a set of PHP scripts (with source code, modification allowed).

Users can receive, view, manage, compose and send email through web interface (POP3, IMAP, and SMTP supported). Mails are organized in Inbox/Sent/Drafts/Trash and user-defined folders. Supports multiple attachments, predefined and custom skins, remembers read/unread message status, provides Address Book, DHTML Rich-Text editor, account management and individual settings for each user, spam filters, user-specified time zones, international charsets, etc. Correctly and safely displays HTML mail. Properly decodes and displays messages that use international charsets.

Supports modern AJAX interface (for IE6/IE7/Firefox/Safari/Opera) and classic HTML view (for older browsers).

Flexible mail storage: mails can be stored in database (completely or headers only) or always be taken directly from the mail server (Direct mode).

Web-based administration (detailed administrator's guide included).

Integration with existing systems: can bypass initial login screen and accept user account data from another application rather than from user input.

A number of localizations is shipped with the product. Can be easily translated to other languages if needed.

Can be used with MS SQL Server or MySQL database.