What is SMTP?

Computer NetworkInternetMCA

SMTP represents Simple Mail Transfer Protocol. SMTP is a set of interaction guidelines that allow the software to transmit electronic mail over the internet, referred to as Simple Mail Transfer Protocol.

The main objective of SMTP is used to set up communication rules between servers. The servers have a way of recognizing themselves and announcing what kind of communication they are trying to perform. They also have a way of handling errors such as incorrect email address. For example, if the recipient address is wrong, then receiving a server reply with an error message of some kind.

Working of SMTP

SMTP is an end-to-end delivery in which an SMTP client machine contacts the destination host's SMTP server directly to deliver this mail. Unlike the store and the forward principle that provides the mail content to the destination host through several intermediary nodes in the same network, SMTP continues the mail content being sent until it has been successfully copied to its SMTP.

SMTP maintains only delivery to the mail-gateway host, not to the actual destination host, located beyond the TCP/IP network. In the mail gateway, the SMTP end-to-end transmission is hosted to the gateway, gateway to host or gateway-to-gateway. SMTP does not determine the format of mail beyond the gateway.

Each message of the SMTP contains the following field:

  • A header or envelop a null line terminates that.
  • Contents − Everything after the invalid or blank line is the message body with a sequence of lines containing ASCII characters.

Simple Mail Transfer Protocols represents a client/server protocol. The client SMTP device initiates the session by sending an SMTP message, and the mail server responds by receiving an SMTP message to the session request.


There are various problems in SMTP which are as follows −

  • Some older implementations are not capable of handling messages longer than 64 KB.
  • If the client and server have multiple time-outs, they may give up when the other is still busy. This will terminate the connection unexpectedly.
  • In rare situations can trigger infinite mail storms.
Updated on 04-May-2021 13:38:28