[Mimedefang] Re: Non-routable addresses in HELO

Jan-Pieter Cornet johnpc at xs4all.nl
Wed Jul 12 05:23:02 EDT 2006

On Tue, Jul 11, 2006 at 02:30:22PM -0400, Paul Russell wrote:
> 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.

Ah, we have slightly conflicting definitions of "legitimate".

I meant: A mail server that doesn't send out spam, and does send
you relevant email.

You meant: A mail server that follows most of the RFCs or at least
the best common practice nowadays.

The truth, as usual, lies in the middle. However where anyone draws the
line is up to them. Strictly following all RFCs to the letter will cause
you to block a lot of non-spam ("wanted") email, and will make you
educate a lot of mail admins. It will also make you unpopular (just look
at rfc-ignorant.org).

Not blocking misconfigured crappy servers makes you drown in junk, but
hey, at least you don't miss that one unexpected business offer that
will make you a fortune and that would have gone away if you had blocked
it! (if you can find it amid all junk)

Jan-Pieter Cornet <johnpc at xs4all.nl>
!! Disc lamer: The addressee of this email is not the intended recipient. !!
!! This is only a test of the echelon and data retention systems. Please  !!
!! archive this message indefinitely to allow verification of the logs.   !!

More information about the MIMEDefang mailing list