Simple Mail Transfer Protocol is a technology that have been introduced to simplify the process of communication, either for personal purpose or for professional use. The emergence of technological tools and devices have made the conduction of several processes much more easier that before. One such device is computer, with internet connection activated on it. The internet connection facilitates the emailing function with utmost efficient. SMTP servers have a very significant role to play as far as the sending and receiving of the emails are concerned. Due to the evolution of these technologies, an individual does not any more need to wait too for long to get his messages sent to the recipients. Server SMTP is the component that facilitates instant messaging process.

There was a time when people used to write letters to their loved ones living far away from them. An email is no different from a letter. With the same writing format, an email appears to be the advanced form of letter writing. The main difference is in terms of the time taken for communicating with the people. Letters took days, weeks and even months to get delivered to the recipient, but with the help of SMTP servers, emails get delivered instantly. Not only this, but the server SMTP also sends the confirmation message to the sender stating that the message has successfully reached the recipient.

Emails are no longer limited to personal usage, in fact, they have also become one of the best modes of communication within the official or business edifices. It makes the interaction between the senior management and the employees as well as between the business owners and the customers much more convenient. Thus, it becomes essential that the emailing function is carried out well. The proper conduction of the task is ensured by the SMTP servers installed. From sending the emails to delivering it, there is a series of steps that is followed by the server SMTP. As soon as the sender clicks the send button, the server checks the recipient's DNS (Domain Name Registration) and then verifies whether the specified address is valid.

Once confirmed about the validity of the address, the server SMTP interacts with the recipient's server and informs it about the waiting message. The server then accepts the mail and thereby triggers a confirmation message to the sender's computer. On most of the PCs, the SMTP servers use a program known as sendmail for the actual process of sending message. The series or queue of steps that surrounds the whole process is termed as sendmail queue. This is the program that tries to resend the message every 15 minutes, in case it fails to reach the recipient. If even after five days, the message remains undelivered, it triggers a mail to you stating the inconvenience.

Human languages cannot control these technical processes. Thus, certain commands are used by the server SMTP to carry out the email delivery functions relevantly. Within the sendmail program, these commands have been inbuilt so that the system can easily conduct the emailing procedures. Some of the common commands that the SMTP server use include HELO, MAIL FROM, RCPT TO, DATA, RESET, QUIT, and many more. Proper usage of these commands facilitate the step-wise functioning of the emails delivery service.