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In the diagram displayed above, the elements include:
* A '''user'''. That's the person who wants to send an email.* An '''MUA ''' (email client). This is the application the user uses to send an email. It can be a native application or a web application. We'll set up both types.* Two '''MTAs'''. These are the servers responsible for getting your emails to the <u>destination </u> server.** They are similar to routers (whcih which route packets) but work on the <u>application </u> layer rather than the <u>network </u> layer.** In our example , there are only two MTAs - but there can be several.** You connect to your MTA over a <u>secure </u> connection, so your emails can't be read by the operators of the network you're connected to.** The mail message then travels the rest of the way to the destination MTA the emails travel completely <u>unencrypted</u>, so anyone with access to the routers in -between can read all your emails. This That is why many organizations will refuse to send you confidential information over email.
* The LDA/MDA will receive the email from the MTA, and will store it on disk in some format. MailDir and MBOX are the most popular mailbox formats.
* When sending an email you send it to the destination using your MTA, but you also want to save it in your "Sent" folder for yourself. This is accomplished by a separate connection to your IMAP or POP3 server.
