A program used to read and send email messages. As opposed to the email server, which transports mail, an email client is what the user interacts with. Some examples of these are: Outlook, Outlook Express and Netscape Messenger.
An Email client is a program that allows you to connect to your mail server (i.e. Outlook, Eudora) and retrieves your email for you to read and manage.
The software your computer uses to access your e-mail, for instance, Microsoft Outlook.