Simple Mail Transfer Protocol And How It Works


SMTP or Simple Mail Transfer Protocol is the protocol which is mainly used to send the email over the internet. The email clients on your computer such as Eudora, Outlook or Mac OS X Mail are generally using this SMTP in order to send the email message to the mail server. Then the mail server uses this same protocol to relay that the message to the exact receiving mail server.

What is SMTP?

Basically, the SMTP or simple mail transfer protocol is the set of commands which authenticate and also direct the transfer of emails. When configuring the settings for your electronic mail program, you in fact require a set of SMTPs to the SMTP settings of your local ISP (Internet Service Provider). On the other hand, the incoming mail server, such as POP3 or IMAP must be set to the server of your mail account that might be different than the SMTP server. It is also a TCP/IP protocol for sending and receiving the email messages. It is only limited in its ability to queue the messages at the receiver end.

It is probably used with 1 of 2 other protocols such as IMAP or POP3 which allows the users in order to save the messages in the mailbox on the server and you can also periodically download them from the server. This particular protocol is usually implemented to operate over the internet port 25. An alternative to this simple mail transfer protocol which is widely used is X.400. Most of the mail servers are currently supporting the extended simple mail transfer protocol (ESMTP) that allows multimedia files to be delivered as the electronic mail (E-mail).

How SMTP works?

  • All modern email client programs currently support SMTP. When it comes to the SMTP settings, they are maintained in an email client, including the IP address of the simple mail transfer protocol server.
  • The internet based clients insert the SMTP server address inside their configuration while system clients, providing the settings of SMTP which allows the users in order to specify their own choice of server.
  • The physical SMTP server might be highly dedicated to provide the email traffic service only, but it is frequently combined with at least POP3 protocols and sometimes any other proxy server functions.
  • In order to have the standard communication, SMTP usually runs in the top of the TCP/IP protocol and also uses the TCP port number 25.
  • The standards groups also have designed TCP port 587 to provide a greater support to the specific aspects of the protocol and also improve SMTP & help combat spam on the web.

As SMTP is completely based on the client-server model, it is also considered to be the simple ASCII protocol. Once a TCP connection established, the email sending machine is operating as the client and waits for the receiving machine that is operating as the server. The server first begins a connection by sending a text message and asks whether the client is ready to receive the mail. If not, the client releases a connection and tries again.