[Mimedefang] Re: Non-routable addresses in HELO

Paul Russell prussell at nd.edu
Tue Jul 11 14:30:22 EDT 2006

On 11 Jul 2006, Jan-Pieter Cornet <johnpc at xs4all.nl> wrote:
 > Also note that I'm not aware of any SMTP server implementation that
 > actually enforces syntactic checks on the HELO or EHLO argument out
 > of the box (resulting in lots of clients sending utter crap). Also
 > note that blocking based on EHLO will produce some false positives:
 > there are legitimate mail servers out there that EHLO as, eg.
 > "lan.local" or something silly.

Any mail server that is so poorly administered that is not offering a properly
formatted HELO argument is not legitimate and should not be connected to the
Internet. The RFC clearly states that the server *MUST* use a FQDN or bracketed
literal IP address as the HELO argument. Anything else is explicitly prohibitted
and grounds for rejecting the connection.

Paul Russell, Senior Systems Administrator
OIT Messaging Services Team
University of Notre Dame
prussell at nd.edu

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