All email accounts include webmail access using 3 clients:
Horde

Users can read, send and organize email messages and manage and share calendars, contacts, tasks and notes.

RoundCube

RoundCube Webmail is a multilingual IMAP client. It provides full functionality, including MIME support, address book, folder manipulation, message searching and spell checking.

SquirrelMail

SquirrelMail has all the functionality you would want from an email client, including strong MIME support, address books, and folder manipulation.