In this day and age, billions of pieces of information are sent across the internet per day. This exchange of information is vital for all the technology and computationally intensive activities we all engage in like surfing the web on a computer or building programs to compute and conduct research. One particularly important part of modern life is emails: they are used in business communication, marketing campaigns, personal connections, and many more. How do emails get sent between people? The answer is SMTP protocol.
What is SMTP protocol? SMTP stands for Simple Mail Transfer Protocol. Put simply, it’s a method for sending different emails. It’s powerful because it standardizes the process of sending emails across diverse computers, hardware setups, etc… This serves to make email exchange in its modern sense possible. In order to better understand the SMTP protocol system, let’s first look at an SMTP server. It’s a mail server that sends and receives emails using the SMTP protocol. These can be run either locally or on the cloud. How does this process look? Firstly, a TCP connection is opened between the Mail User Agent, which is the email client/application used to send and receive emails, and the destination email server. The client then sends a series of commands and the contents of the email. The server runs another program called the Mail Transfer Agent to authentify and find the location of the destination server and then send it. Finally the data is transferred, the server is alerted of the finished transmission, and the connection is closed. Note that emails aren’t directly sent to the intended recipient. There is often a chain of several different SMTP servers before the contents of the email are finally sent to the intended recipient’s email server. This ensures that the contents of emails are harder to intercept and track.
Once the contents of the email reach their final destination email server, there is still some more processing needed. First we can consider the port position where the information is being transferred. What are ports? Ports represent the concept of “virtual addresses” where network information can be sent in and out of. Specifically, the SMTP protocol can use port numbers 25, 465, 587, and 2525. Once the email is sent to the final destination server, the IMAP (Internet Message Access Protocol) and Post Office Protocol (POP) to retrieve emails from this final destination in the chains so that it may be displayed to the user in their email inbox. Nowadays, a more general and powerful form of SMTP is utilized called ESMTP (Extended Simple Mail Transfer Protocol). ESMTP enables the sending of attachments and provides other more powerful capabilities than SMTP. For this reason, SMTP isn’t actually utilized much these days.
The Simple Mail Transfer Protocol (SMTP) is a simple yet foundational information transfer protocol that enables the quick and effective email exchange that we all take for granted today. It is thus important for technology enthusiasts to have a solid understanding of this concept to further fuel and power our understanding of the Internet and technology in general.