On Tue, Sep 02, 2003 at 06:51:59PM +0100, Colin Watson wrote:
> Just wondering what this error (Helo Command Rejected: Host not found) was referring 
> too? I receive it in sendmail on messages I'm trying to fire off. I suspect (but 
> have been unable to confirm) it may be reverse DNS related?

Yes, probably.  I suspect that this is the result of the latest move
in the war-against-spam-and-viruses.  A number of ISPs and other mail
system administrators have developed a policy of being hard-line about
the name a system uses to announce itself when connecting to their
SMTP servers.  Typically that is the argument to the 'HELO' or 'EHLO'
command which is the opening line in the SMTP dialog.  Some admins go
even further and require that the name given in the HELO line
corresponds to the IP number the connection was made from.

The idea is that this name should be a fully qualified, resolvable
domain name, or possibly an IP address.  Generally that will
automatically be the case if you're running one of the standard Unix
MTAs on the open Internet, and have a correctly configured DNS zone
file.  However, if you're behind a NAT gateway or using a private DNS
address space, then you might have trouble.

With sendmail(8), you can override the default choice, which is just
the FQDN of the server, by setting:

    define(`confDOMAIN_NAME', `smtp.example.com')dnl

in your `hostname`.mc file.

Note that this has nothing to do with what appears after the @ sign in
any e-mail addresses dealt with by your server.  It's effectively the
hostname of the server itself that should be entered there.



Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
PGP: http://www.infracaninophile.co.uk/pgpkey         Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK

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