What is the role of the HELO (or EHLO) command in SMTP?

The HELO (or EHLO) command plays a crucial role in the Simple Mail Transfer Protocol (SMTP) by initiating the mail transfer process between the client and the server. When an SMTP client connects to a mail server and wishes to send an email, it uses the HELO command to identify itself. This identification is important for establishing a communication session and signaling to the mail server that the client is prepared to send an email message.

Additionally, using the EHLO variant allows the client to request information about the server’s capabilities, such as supported extensions and methods. However, the essential function of both commands at their core is to establish a relationship between the client and server and commence the SMTP session, marking the beginning of mail transfer.

Other options focus on different functionalities within the SMTP protocol but do not capture the primary purpose of the HELO/EHLO commands. For instance, specifying the recipient's address pertains to the MAIL FROM and RCPT TO commands, terminating the connection relates to the QUIT command, and requesting capabilities aligns with the use of EHLO but not solely with the initiation of mail transfer. Therefore, the role of the HELO (or EHLO) command primarily serves to kick off the mail transfer process.