What is the SMTP HELO/EHLO clause?

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Question

The SMTP protocol is discussed breifly in Q0344: What is SMTP? What exactly is the HELO and EHLO clause?

Answer

The SMTP HELO clause is the stage of the SMTP protocol where a SMTP server introduce them selves to each other. The sending server will identify who it is and the receiving server will (as per RFC) accept any given name. There is no requirement to give the correct information at this stage.

Gordano’s GMS Anti-Spam can provide additional security. A number of checks can be performed. For example, running a reverse lookup on the connecting IP address to ensure that it matches up with what the remote servers is claiming.

EHLO is the Enhanced SMTP (ESMTP) version of HELO. ESMTP adds a number of essential additions to the SMTP protocol. When this command is sent, the server will respond with the EHLO options that is supports. Gordano products support a wide range of ESMTP options to provide optimal use of bandwidth, reduce latency of message transport and improve error handling.

If a server does not support ESMTP it will respond with an error and the sending server must revert to plain, simple SMTP in order to send the message. However, all the advantages of ESMTP are lost.

Keywords:RFC821 821, SMTP, HELO, EHLO, protocol

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