Re: Blacklist usage in zmailer

["Alexey Lobanov" <Alexey.Lobanov@cpr.spb.ru>]

Hello.

On 29 Aug 2002 at 20:58, Tomaz Borstnar wrote:

> At 11:13 29.8.2002 -0300, Rik van Riel wrote the following message:
> >As an aside, I'm also thinking of adding an option to
> >smtpserver to refuse email when the HELO string doesn't
> >resolve ;)

> Bad, bad, bad. You wont like the results probably. Or you dont care about 
> lost mail? Not all of that is spam, you know?

Postfix does have quite full set of HELO rules:

#   reject_non_fqdn_hostname: reject HELO hostname that is not in FQDN form
#   reject_invalid_hostname: reject HELO hostname with bad syntax.
#   reject_unknown_hostname: reject HELO hostname without DNS A or MX record.

My experience shows that first rule is OK. Only client (and spammer) 
workstations say "HELO Default", etc. Naturally, direct or authorized clients 
bypass checking. But even the second rule is too restristive for guests: about 
50% of legitimate corporate MS-Exchange servers compose their self-names from 
NetBIOS name (where underscore "_" is a must according to MS traditions) and 
valid domain. So, neither formal nor real DNS-compliance tests are feasible.

Alexey

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