[RFCI-Discuss] about FQDN for our smtp servers

[Derek J. Balling]

On Apr 12, 2006, at 5:23 AM, Alan Brown wrote:
> The RFC has a MUST NOT clause associated with non-resolving HELO
> entries, which makes this claim arguable.

RFC2821 says:

    An SMTP server MAY verify that the domain name parameter in the EHLO
    command actually corresponds to the IP address of the client.
    However, the server MUST NOT refuse to accept a message for this
    reason if the verification fails: the information about verification
    failure is for logging and tracing only.

reason = "the domain name parameter in the EHLO command actually  
corresponds to the IP address of the client"

So, you MUST NOT refuse simply because [ reverse(connectingIP) !=  
HELOarg ]

However, there's no clause that stops you from rejecting on any other  
criteria, such as a server violating :

    The domain name, as described in this document and in [22], is the
    entire, fully-qualified name (often referred to as an "FQDN").  A
    domain name that is not in FQDN form is no more than a local alias.
    Local aliases MUST NOT appear in any SMTP transaction.

If you can't resolve it from the server side, it's a local alias of  
some sort, in which case it doesn't match the definition of "Domain"  
used by the RFC, making the EHLO/HELO argument syntactically invalid.

Cheers,
D




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