It is an oft-touted proverb that necessity is the mother of invention. It holds true in every arena under the sun. SMTP or simple mail transfer protocol is also invented to satiate our requirements. It is a de factor standard that accelerates the e-mail transmission. When you send emails, they first reach the server that communicates with the sender's computer through SMTP protocol. Prior to implementation of this standardized protocol, mail sending was handled through a series of complicated steps. Delayed delivery of the emails was of great problem to both mail senders and receivers. All these problems were sorted out as soon as SMTP became an established format of mail transmission.
Though the new protocol too consists of a series of some adhesive steps but they are easy to understand. Mail delivery has become faster too. Moreover, the protocol is easy to install. So, SMTP is offering multiple benefits to the mail senders and this is the reason it has become quite a popular choice all around the globe. With an accelerated performance delivered by this protocol the email senders experience a hassle-free and quicker mail delivery. Such an enhanced service of this newly developed mail transfer mode helps the mail senders communicate with the receivers in twinkling of eye.
This protocol is text-based. For an effective and quick communication, it contains a set of limited commands as well as reply codes. SMTP is explicitly defined in RFC 2821 simple mail transfer protocol. It completely relies on an efficient data connection and is never influenced by a typical transmission subsystem. The SMTP server communicates with the outer world with help of port 25 though nowadays this connection is built up using other ports such as 2525.
There are only ten commands in the SMTP protocol. These commands are the language both the client and server use to communicate with each other. When the commands are sent from the client to the SMTP server, reply comes in the form of both text messages and numerical codes. These codes signal the clients whether the previous commands are successfully sent or not.
Both the commands and replies comprise of the ASCII characters. Each of the commands is four characters in width and sometimes is paired with the additional sub commands. The reply code always consists of three digits. The numerical figure is followed by the text. The length of the text varies depending on the mail server in use. Normally this length is restricted to 100 characters but can stretch up to 508 characters. Space is inserted to separate the numerical and text characters. The most common of these commands is HELO and EHLO. Both of them are used for identification of the sender. HELO is older one and is used in case of basic functions. For more advanced functionalities, the client uses EHLO command. When this new command is used, the
SMTP server gets into the extended mode to allow the client to use the advanced commands. It is a good news that the majority of the
SMTP servers are designed to support the EHLO command.
