[RFCI-Discuss] about FQDN for our smtp servers

[Alex van den Bogaerdt]

On Tue, Apr 11, 2006 at 08:00:28PM +0200, mouss wrote:

> >> some MTAs will reject you you if
> >>your helo doesn't resolve.
> >>    
> >
> >So is this.(*)
> >  
> This is debatable. The RFCs are self-contradictory here (one RFC 
> requires clients to use a "canonical" name, but doesn't allow servers to 
> check for that). of course, even requiring helo has been controversial 
> for some time...

This has come up here before.  Your statement is false in multiple ways.

Indeed, >>something<< is not allowed by this RFC.  But people seem
to think it means you cannot do >>anything<<.  That isn't right.

1: It is most certainly allowed to verify the provided parameter.
2: One must not refuse to accept a message if the verification fails.

In step 1 you gain some knowledge.  You cannot use this knowledge
to refuse to accept the message.  This is what the RFCs forbid.
The "MUST NOT" refers to a specific part of the RFC, not to anything
you can come up with.

The parameter must be a resolvable, fully qualified domain name
FOR THE CLIENT HOST.  If this client host claims to be somebody
I know it is not, using knowledge I possess, I can safely reject
the message(s) in that session.

People claiming you cannot refuse messages based on HELO are
RFC ignorant themselves.

Alex