SMTP (Simple Mail Transfer Protocol) is a protocol for transmitting electronic mail (email) messages between servers. Most email systems that send mail over the Internet use SMTP to send messages from one server to another, and to deliver messages to local mail clients like Microsoft Outlook or Apple Mail.
SMTP is a relatively simple protocol that uses a set of commands and responses to transmit email messages between servers. When you send an email message from your client (such as Microsoft Outlook or Apple Mail), your client first connects to an SMTP server and sends the message using the SMTP protocol. The SMTP server then delivers the message to the recipient's email server, using the SMTP protocol to transmit the message across the Internet.
The SMTP protocol includes a set of commands that can be used to send and receive email messages and manage email accounts and servers. Some common SMTP commands include:
- HELO: used to identify the sending server to the receiving server
- MAIL FROM: used to specify the sender of the message
- RCPT TO: used to specify the recipient of the message
- DATA: used to send the actual message contents
- QUIT: used to terminate the SMTP session
SMTP is just one part of the overall process of sending and receiving emails. It is typically used in conjunction with other protocols like POP (Post Office Protocol) or IMAP (Internet Mail Access Protocol), which are used to retrieve email messages from a server and store them locally on a client.
How SMTP works (simplified)
Imagine that you are sending a letter to your friend Tom, who lives in a different city. You would normally put the letter in an envelope, address it to Tom, and put a stamp on it. Then, you would drop it off at the post office, and it would be delivered to Tom's mailbox.
Sending an email is similar to this process, except that instead of a physical letter, you are sending a digital message. The message is sent from your computer (which is like your home) to an SMTP server (which is like the post office). The SMTP server then delivers the message to Tom's email server (which is like his mailbox). Finally, Tom's email client (which is like his mailman) retrieves the message from the email server and delivers it to Tom.
SMTP is like the set of rules and guidelines the post office follows to ensure that the letter is delivered to the right place. It specifies things like the sender's and recipient's addresses, the message's subject, and the message's body.
SMTP servers are like the post office workers who handle the delivery of the letter. They use the SMTP protocol to transmit the message between servers and ensure it is delivered to the correct recipient.
An SMTP server is like a more efficient and reliable post office. It can help to increase the chances that your message will be delivered successfully and provide you with additional features such as tracking and analytics.