Key Points
- Simple Mail Transfer Protocol, or SMTP, was one of the first commercially available protocols that determined how electronic messages — including emails and files — were sent.
- There are two types of SMTPs. One involves sending the content directly (end-to-end), and one involves storing it for later sending (store-and-forward). End-to-end is used for communication outside of networks, while store-and-forward is used within networks.
- Despite the fact that SMTP is more than thirty years old, it is still a wildly popular protocol that is used when sending Emails.
- Simple Mail Transfer Protocol is not the only email protocol that is used today. Other examples include IMAP and POP3.
- Simple Mail Transfer Protocol can be used for sending any electronic data on the internet, including texts, pictures, videos, links, and more.
Simple Mail Transfer Protocol is an electronic mail protocol. This means that it is responsible for ensuring that electronic networks can talk to each other and send data back and forth in the form of electronic messages. Specifically, it sets the procedures by which two servers Message Transfer Agents can talk to each other and exchange data.
Simple Mail Transfer Protocol was one of the first commercially available protocols that determined how electronic messages were sent. There are two types of SMTPs. One involves sending the content directly (end-to-end), and one involves storing it for later sending (store-and-forward). End-to-end is used for communication outside of networks, while store-and-forward is used within networks.
Quick Facts
- Created
- 1980
- Creator
- Jon Postel
- Original Use
- Procedure to facilitate electronic messaging and the electronic exchange of data
- Cost
- None.
Simple Mail Transfer Protocol: History
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Simple Mail Transfer Protocol was invented in 1980 by John Postel and first became widely used in 1981. It is an electronic mail protocol which is responsible for ensuring that electronic networks can talk to each other and send data back and forth in the form of messages.
Simple Mail Transfer Protocol creates the specific procedures which are required by the two servers to allow them to exchange data. It also allows different computer networks to communicate with each other and exchange electronic data such as messages and files.
When it was developed, SMTP replaced the File Transfer Protocol. It was allocated port number 57 and its widespread adaptation quickly began. Electronic mail agents soon began to appear and SendMail was one of the first companies to use Simple Mail Transfer Protocol. However, security concerns eventually made SMTP out of date, and the system evolved into other versions, such as EMSTP and POP3.
Simple Mail Transfer Protocol: How it Works
A modern flow chart can easily be understood to determine how SMTP works. For example:
- A user is at their computer and using any number of Email services, such as Gmail or AOL. They type an Email and click the send button.
- The Email enters the user’s send queue on their own server. If it is a normal personal commercial user, the queue is likely not particularly long, and the Email is sent quickly.
- The Email arrives at a Message Transfer Agent, which makes a connection between the Message Transfer Agent of the intended recipient. This occurs via SMTP protocol, which connects those two Message Transfer Agents. It will usually occur on port number 25.
- From there, the Email travels to the intended recipient’s Email inbox, where it can be accessed after it has been downloaded by the recipient’s server.
Simple Mail Transfer Protocol: Historical Significance
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The importance of the development of SMTP cannot be understated, as it was critical to facilitating the advancement of electronic communication between computers. The fact that it is still used today — in largely the same form — also speaks to how useful and powerful the invention of SMTP has been.
That being said, it is important to realize that SMTP was originally designed largely for internal communication between networks and that the protocol had to be expanded and altered in order to make it robust and effective when communicating with other networks. That resulted in the ESMTP, or Extended Simple Mail Transfer Protocol, that first came into existence in 1995.
The success of the Simple Mail Transfer Protocol set the stage for the mass adoption of Email clients. For example, Gmail, Microsoft Outlook, and many additional services simply would not have been commercially viable were it not for the success of SMTP.
Difference Between SMTP, IMAP, and POP3
Although Simple Mail Transfer Protocol is still used by some mail providers, it has largely been replaced by IMAP and POP3. There are a few key differences between these different types of mail protocols which are explained below.
Simple Mail Transfer Protocol functions by sending data between the sender and receiver’s servers. It sends the email from the sender’s email service to the receiver’s inbox. However, IMAP retrieves email messages and allows users to organize the emails on the server.
POP3 works by corresponding with the receiver and their mail service. It retrieves emails and organizes them. It also downloads emails from the server and then deletes the server copies.
