Mail User Agent (MUA)

A Mail User Agent (MUA), often referred to as an email client, is a software application used to access, manage, send, and receive email. It acts as the interface between the user and the email system, allowing users to interact with their email in a user-friendly way. The MUA connects to a mail server to send outgoing mail and to retrieve incoming mail.

It allows users to write and send emails. The MUA formats the email according to internet email standards and then uses the [[Simple Mail Transfer Protocol]] (SMTP) to send the email to a [[Mail Transport Agent (MTA)|Mail Transfer Agent (MTA)]] for delivery.

It retrieves email from a user's mailbox on the mail server. This is typically done using email retrieval protocols like the [[Post Office Protocol]] (POP) or the [[Internet Message Access Protocol]] (IMAP). It provides tools for organizing, searching, and managing emails. This includes creating folders, marking emails as read or important, flagging spam, and filtering.

In the email communication process, the MUA plays a critical role in the user-facing side of email. While the MTA (Mail Transfer Agent) handles the routing and delivery of email between servers, the MUA is what the user interacts with to read and compose messages.

Some examples of MUAs include:

• Desktop Email Clients: Applications like Microsoft Outlook, Mozilla Thunderbird, and Apple Mail are standalone programs installed on a user's computer.
• Web-Based Email Clients: Services like Gmail, Yahoo Mail, and Outlook.com are accessed through a web browser and provide MUA functionality.
• Mobile Email Apps: Applications designed for smartphones and tablets, such as the iOS Mail app and the Android Gmail app.