You have many different webmail options avaliable to you as our client. Each with their own unique look/feel and features(spellchecks, email signatures, layouts, etc..).

The only way to find the best one suited towards Your client or Yourself is to try them all :)

RoundCube - RoundCube Webmail is a browser-based multilingual IMAP client with an application-like user interface. It provides full functionality you expect from an e-mail client, including MIME support, address book, folder manipulation, message searching and spell.
http://YourDOMAINhere.com/webmail

Atmail - Atmail Webmail Software boasts an innovative user interface, pushing the boundaries of the traditional WebMail feature-http://YourDOMAINhere.com/atmail

Squirrel Mail - SquirrelMail has all the functionality you would want from an email client, including strong MIME support, address books, and folder manipulation.
http://YourDOMAINhere.com/squirrelmail



UebiMiau - Uebimiau is an universal webmail developed in PHP
http://YourDOMAINhere.com/uebimiau

Replace "YourDOMAINhere.com" with your proper current domain.