What command is used to specify the sender’s email address in an SMTP transaction?

In an SMTP transaction, the command used to specify the sender's email address is vital for establishing the origin of the email. The MAIL FROM command clearly indicates the email address of the sender. This command is the first step in the process of sending an email and is essential for ensuring that the recipient knows which address the message is coming from.

By using the MAIL FROM command, the sender's email address is communicated to the receiving mail server, which is important for both delivery and for potential bounce-back messages if delivery fails. Other commands in the SMTP protocol serve different purposes: HELO identifies the sending server to the receiving server, RCPT TO designates the recipient's address, and DATA begins the transmission of the actual message content. Each plays a distinct role in facilitating email communication, but only MAIL FROM is specifically used to identify the sender.