How does a mail server work?

How does a mail server work?

A mail server (sometimes also referred to an e-mail server) is a server that handles and delivers e-mail over a network, usually over the Internet. A mail server can receive e-mails from client computers and deliver them to other mail servers. A mail server can also deliver e-mails to client computers. A client computer is normally the computer where you read your e-mails, for example your computer at home or in your office. Also an advanced mobile phone or Smartphone, with e-mail capabilities, can be regarded as a client computer in these circumstances.

Using email address has become a common phenomenon in today’s world. From sending to receiving an email there are a lot things are happened in background.
That whole process can be divided into two steps:
They are - Sending mail and receiving mail.  And the two protocols of this process are given below:

>> Sending email: Simple Mail Transfer Protocol (SMTP)

>> Receiving email: Post Office Protocol (POP) / Internet Message Access Protocol (IMAP)

Key players in mail transection:

The following key players are important in understanding the operation of a mail server.

• Mail User Agent (MUA): The MUA is a component which interacts with end users directly. Examples of MUA are Thunderbird, MS Outlook, Zimbra Desktop. Web mail interfaces like Gmail and Yahoo! are also MUA.
• Mail Transfer Agent (MTA): The MTA is responsible for transferring an email from a sending mail server all the way to a recipient mail server. Examples of MTA are sendmail and postfix.
• Mail Delivery Agent (MDA): Within a destination mail server, local MTA accepts an incoming email from remote MTA. The email is then delivered to user's mailbox by MDA.
• POP/IMAP: POP and IMAP protocols are used to fetch emails from a recipient server's mailbox to recipient MUA.
• Mail Exchanger Record (MX): The MX record is the DNS entry for mail servers. This record points to the IP address towards which emails should be shot. The lowest MX record always wins, i.e., gets the highest priority. For example, MX 1 is better than MX 2. The IP address of the MX record may vary based on the design and configuration requirements, as will be discussed later in the article.

When a sender clicks on the send button, SMTP (MTA) ensures end to end delivery of an email from a sender-side server to a destination server. Upon reaching the destination server, the MTA local to the destination server accepts the email, and hands it over to the local MDA. The MDA then writes the email to a receiver's mailbox. When the recipient checks for emails, they are fetched by MUA by using protocols like POP or IMAP.