[CentOS] Re: postfix tightening

[Gavin Carr]

On Sat, Apr 02, 2005 at 03:54:37PM -0600, Les Mikesell wrote:
> > Anyway, the point of checking that a system that's trying to deliver
> > email to you has a name that resolves to the address it's using, that
> > that address resolves back to the name, and that the HELO specifies
> > the correct name as well, is that most privately owned Windows PCs
> > don't fulfill those requirements.
> 
> There is no requirement for the HELO to match anything else.  It must
> be syntactically correct but it does not have to have anything to do
> with the particular interface you happen to be using.  On the other
> hand the From: address does have to be resolvable - otherwise you
> wouldn't be able to reply anyway.

Wrong. RFC2821 says:

4.1.1.1  Extended HELLO (EHLO) or HELLO (HELO)

   These commands are used to identify the SMTP client to the SMTP
   server.  The argument field contains the fully-qualified domain name
   of the SMTP client if one is available.  In situations in which the
   SMTP client system does not have a meaningful domain name (e.g., when
   its address is dynamically allocated and no reverse mapping record is
   available), the client SHOULD send an address literal (see section
   4.1.3), optionally followed by information that will help to identify
   the client system. The SMTP server identifies itself to the SMTP
   client in the connection greeting reply and in the response to this
   command.


Cheers,
Gavin

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