E-mail: User Agent
A mail user agent (MUA) is a program that allows you to receive and send e-mail messages; it’s usually just called an e-mail program. To use an MUA such as Eudora or Microsoft Outlook, you install the MUA program on your computer and then use it to download and store e-mail messages to your computer; it will also allow you to read or write messages offline. Web-based MUAs, such as Hotmail and Yahoo, store messages on their own mail servers and allow access to them through a Web page. An MUA is sometimes called an e-mail agent or an e-mail client.