On Wed, Oct 31, 2001 at 10:29:51AM -0800, Jeremy C. Reed wrote:
> 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.
Note that of course nothing says that the IP literal or the FQDN have to be
resolvable or reachable by the receipient (in case you send a mail from
behind a masquerading firewall)
So, if you try to validate the value given there, you will have surprises
(it's a bit like ident, you can use the value for debugging if a meaningful
one is given by the remote host, but you can't depend on it to accept mail)
Marc
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