Simple Mail Transfer Protocol (SMTP) Review

Most of the internet systems and internet service providers (ISP) are using the SMTP as a method to transfer the mail message from one end to another. It is considered to be the push protocol and thus it is used to send the email whereas IMAP (Internet message access protocol) and POP (Post Office Protocol) are used to get such emails at the receiver end. At present, email or electronic mail is the most emerging and also most valuable services on the internet.

Fundamentals of SMTP:

Simple mail transfer protocol or SMTP is actually an application layer protocol. The client who wishes to send the email message opens the TCP connection to SMTP server. You can buy SMTP servers online. Then, the same will send the email across the connection. This SMTP server in the connection is always on the listening mode. This is why it will give the very fast listening for the TCP connection from any user. This process of using simple mail transfer protocol initiates the connection on the port number 25. After the TCP connection has been successfully established, the client can able to send your mail message in an instant manner to any of your preferable recipient. SMTP is also considered to be the regularity for the transmission of emails on the web platform. It is generally used by the server system to send and receive the emails but the host based application in the client side only uses the same protocol to send the mails to the email server. For the receiving purposes of the electronic mails, the client systems are using the IMAP or POP3. 

Model of SMTP system:

In the entire model of the SMTP system, the users are dealing with the UA (User Agent) such as Netscape, Outlook, Mozilla, Chrome, etc. MTA is actually used for the exchanging process of the mail with the help of TCP. The mails to be sent by the users don’t have to deal with this MTA. This is because it is the responsibility of the system admin in order to setup the local Message Transfer Agent (MTA). This message transfer agent maintains the small array of mails so that it will make a schedule to repeat the process of mail delivery in case the receiver is not available in the opposite end. It also delivers the electronic mail message to the mailboxes and the details will then be downloaded later by the UA. Both the SMTP server and SMTP client should have two important components such as,

  • Local MTA
  • User Agent (UA)

Both these significant components are really very helpful for sending and receiving the mail messages between the sender & receiver. 

SMTP protocol:

The model of SMTP protocol usually is of two types such as,

  • End to end method
  • Store and forward method

When it comes to the end to end method of SMTP protocol, it is mainly send to make a communication between the various companies. The store & forward method is used within the organization. If any person wants to send the email and it will communication to the host SMTP of the destination directly for sending the mails to the correct end. When considering the SMTP server, it will save your mail until it is efficiently copied to the SMTP receiver end. 

During the process of sending and receiving the mail messages between the senders and receivers, the different types of commands used by the server and client systems. The following are some of the popular SMTP commands such as,

  • HELO – This command is mainly used to identify the client system to the SMTP server. Similarly, it is completely qualified domain name and will be sent only once in a session. 
  • RCPT – It follows MAIL command and helps to find the addressee usually the completely qualified name of the addressee. It is also very helpful to find the multiple addressees by using this command.
  • MAIL – It is very useful to start the mail transfer and entirely qualified domain of the originator. 
  • DATA – This command is used to send the data line by line.

The server and client systems are using this SMTP protocol which is the set of communication guidelines to allow and transmit the emails over the internet.