A mail user agent (MUA) is
|“||[a] mail client application used by an end user to access a mail server to read, compose, and send email messages. Common MUAs include Microsoft Outlook and Mozilla Thunderbird.||”|
|“||a software component that allows an end user to compose an email message and send it to one or more recipients.||”|
Most end users interact with their email system via a MUA. A MUA allows an end user to compose an email message and send it to one or more recipients. The message is then sent to a server for further processing (either final delivery or transfer to another server). The MUA is also the component used by end users to access a mailbox where emails have been delivered. MUAs are available for a variety of systems including mobile hosts. The proper secure configuration for an MUA depends on the MUA in question and the system it is running on.
MUAs may utilize several protocols to connect to and communicate with email servers. There may also be other features as well such as a cryptographic interface for producing encrypted and/or digitally signed email.
- "Overview" section: NIST Special Publication 800-177, at 3.