What is a Mail User Agent (MUA) ? Tldr; a mail Client

About

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

A MUA can:

• read and write in the mailbox
• and send emails (by handing them off to the Smtp server (Mail Transfer Agent))

List

Gui

• outlook
• gmail
• Gmx
• Thunderbird (windows, mac, linux)
• Evolution
• KMail

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]

• Mailx (known as mail)
• pine
• mutt
• elm

Library

• Java - Jakarta Mail (JavaMail)
• Java: https://github.com/HubSpot/NioSmtpClient - netty based

Management

Which client has created the mail

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

Example:

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.