SMTP stands for Simple Mail Transfer Protocol. It is a worldwide standard for transmitting email to receiving email. Mainly, IMAP (Internet Message Access Protocol) is used. In the early 1960s, one-on-one email communication was used. People used specific mainframe systems for this. As more computers were introduced into the network as the Internet developed, some standards were developed to allow users of different systems to communicate via email. SMTP was found and grew in the 1970s from one of these standards.
SMTP Features
In addition to simply transferring messages from server to server, SMTP also has some extra features. Some of them are described below.
Mail Relay: Since SMTP was widely used to route emails from one server to another before reaching your server. But now emails are transferred directly from the sending server to the receiving server using DNS MX records (to verify the recipient's SMTP address)
Mail Forwarding: This is not just forwarding like any other email forwarding but it is the ability to transfer emails from any non-local server to an appropriate destination. If a user uses one company's mailbox and moves to another company, the company will not allow the user to log in to the server, but will forward any incoming email to the user's personal mailbox.
Address verification: SMTP uses a “verify” command to verify the existence of the email address before sending an email.
Security: SMTP servers support TLS (Transmission Layer Security) to encrypt the communication channel.
How SMTP works
SMTP works similarly to MTA (Mail Transfer Agent). It supports text/string based transmission and opens port number 25 on the SMTP server. To generate an email, SMTP first checks the configuration of the system from which the email is generated. When this satisfies the requirement (server installation). SMTP uses a technique called forwarding/push to send emails between SMTP servers. It also guarantees email delivery. If the email is not delivered, it will be returned to the sender.
To understand this, we can divide it into several categories.
- Generating email
- Identifying the type of email
- Forwarding
- Storing the email
1.Generating email: To write an email, the user needs an email client application like a browser (Google Chrome). The user types the email server address in the URL bar and opens their mailbox. Finally, the email is written with text and attachments and stored on the mailbox server.
- Identifying the type of email: When the user clicks the send button, SMTP comes into action and identifies the type of email, as SMTP alone does not support attachments such as images and MIME (Multipurpose Internet Mail Extensions) documents. Used as support to extend the functionality of email, Mailbox Server adds the MIME header at the beginning of the transmission. Then the header is identified for any media content.
3. Categorization of email data: After identifying the content of the email, SMTP allows servers (the computers on the network that handle incoming and outgoing email) to divide the data into categories so that the outgoing server can understand how to send the data.
3.Forwarding: After the categorization is done, SMTP sends the email data from server to server, leaving a temporary copy. When the email reaches the destination server, it informs the sender of its delivery. Additionally, information for each server address is stored in the email header, so spam can also be identified.
4. Storing the email: After the email reaches the destination server address, the email is stored in the mailbox. The email remains there as long as the user does not delete it. The user can search the email using the email client applications. The text/media content is then identified and displayed .
When a user wants to send an email (sender) to another user (recipient), the Sender generates an email on an SMTP server like Gmail using a web browser. This email is then identified for attachments and media type content and forwarded/sent to another SMTP server like Yahoo. If a user wants to access that email, the sent email will be stored on the receiving server. POP (Post office protocol) or IMAP can be used to fetch/extract the email.
SMTP application
All major email providers use SMTP to transfer emails between servers like Gmail, Yahoo and Apple. SMTP is widely used on all email servers. The print server also uses SMTP for cloud-based printing.
