An SMTP server (Simple Mail Transfer Protocol) is used to send e-mails across the Internet. Here are the main operating steps of an SMTP server:
1. Connection: When a client (for example, an e-mail software) requests the sending of an e-mail, it connects to the SMTP server. The server responds by sending a welcome message.
1. Authentication: The client must authenticate with the server with a username and password to be authorized to send e-mails.
1. Sending the message: The client sends the message through a specific SMTP command (MAIL FROM). It specifies the sender address, the recipient and the content of the email.
1. Address verification: The SMTP server checks if the recipient’s address is valid and if it accepts emails from the sender.
1. Forwarding the message: If the address is valid, the SMTP server forwards the message to a relay server for distribution across the Internet. If there are multiple recipients, the SMTP server creates a copy of the message for each recipient.
1. Confirmation: Once the message has been successfully transmitted, the SMTP server sends a confirmation to the client, which can then close the connection.
In summary, an SMTP server allows the transmission of electronic messages through the Internet using the commands and protocols specific to SMTP.
