Re: SMTP, 2600, and the security of mail

The lost Bostonian (
Tue, 30 Sep 86 10:29:00 PDT

> From: Mark Crispin <MRC@SIMTEL20.ARPA>

> The Internet protocols are insecure by nature. A reasonably suspicious
> host should always record the host name or IP address of the how which
> actually connected to the SMTP server (the real host, not what was
> claimed in a HELO).

If it is true that all IP implementations enable a server program to
determine the IP address of its peer, then the HELO command, and its
response could be eliminated, which would save us a few bytes.
Certainly the response to the HELO is not necessary, since the server
has already identified itself in the opening greeting.

However, I quote from RFC 821, the explanation for HELO:

        This command and an OK reply to it confirm that both the
        sender-SMTP and receiver-SMTP are in the initial state,
        that is, there is no transaction in progress and all state
        tables and buffes are cleared.

I do not see that there would be a big problem of detecting the initial
state without a HELO. Other protocols (FTP, NNTP) don't use it.


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