Simple Message Transfer Protocol (SMTP) is a protocol that transmits emails over a network; it allows computers and serves to exchange data regardless of their underlying software or hardware. SMTP allows email clients to send messages to your email server; an email or internet service provider may host the server.
SMTP also enable the server to send the email to the recipient’s server’s mailbox. SMTP is a mail delivery protocol, not a retrieval protocol; it standardises how emails move from sender to receiver, making email delivery possible.
So, another protocol, such as IMAP or POP, will be required to retrieve the email from the server.
SMTP differs from IMAP and POP3 because its email-receiving protocol is designed to send emails in a one-way directionality. It can’t fetch messages or receive emails.
How Does SMTP Work?
All email protocols follow a strategic process for sending and receiving emails. SMTP enables the exchange of data between an email client, with whom the user interacts to send and receive emails, and a mail server, which manages the entire process. So here are the steps or processes for sending an email using SMTP between the email client and the mail server.
- SMTP opens a connection between the client and server using a transmission control protocol (TCP).
- The client begins the email-sending process with the specialise ‘hello” command.
- The email client sends the server a series of commands accompanied by the email content, header and additional components.
- Then, the server runs a program called the mail transfer agent (MTA), which checks the domain of the recipient’s email address to see if it matches the sender’s; if it differs, it will query the DNS to find the recipient’s IP address.
- The email client will alert the server when the data transfer is complete, and the server will close the connection.
- Usually, this email server is not the final destination of the email message; the server repeats the SMTP connection with another email server, and the second server does the same; this process continues until the email reaches its final destination.
What is Extended Simple Message Transfer Protocol (ESMTP)?
ESMTP is a more advanced protocol version that expands on its original features and abilities. It enables users to send emails with attachments, use TLS, and access several other capabilities, such as additional commands. Many email clients have adopted this model and stopped using the basic SMTP.