Email - Mail User Agent (MUA) - Mail Client


A Mail User Agent (MUA) is the technical term from a email client application.

User agent in Mail User Agent (MUA) means that it's a user application (known as user agent on the web)

A MUA can:



Command line

  • sendmail - the reference command that you should find on all linux distribution.
echo -e "Subject:Hello World \n\n This is my first mail \n" | sendmail [email protected]



Which client has created the mail

In the header field of an email, search for the value User-Agent


User-Agent: Heirloom mailx 12.5 7/5/10

Where does the name and email of the author come from?

The email internet address is composed of:

  • for the email address:
    • the user login
    • the domain of the hostname or the configured domain in the MTA
  • for the user name: the user name or the user comment

On Linux:

  • the user login may be set in the $USER variable
  • the email address may be set in the $MAIL variable
  • the user login and comment (user name) are in the /etc/passwd file.

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