On Sun, 16 Nov 2003, Manuel Bouyer wrote:

> On Sun, Nov 16, 2003 at 08:50:24PM +0100, Manuel Bouyer wrote:
> > On Sun, Nov 16, 2003 at 07:46:12PM +0100, David Wetzel wrote:
> > > hi folks,
> > >
> > > is it possible to block all hosts that have "dialup" in their full qualified hostname?
> > > how?
> >
> > It's not possible with ipf (this would mean you need a DNS resolver
> > in the kernel).
> > It may be possible with host.allow/hosts.deny.
> > See hosts_access(5).
>
> Hum, I didn't notice your question was sendmail-specific.
> hosts_access(5) is still valid here, but you should also be able to do this
> in the sendmail.cf. I don't know the sendmail.cf language, though.

The more usual way to do what the OP seems to be trying to do, is to
use a DNSBL (DNS Black-Hole List). "dynablock.easynet.nl", for
instance, lists hosts in dynamic blocks who aren't permitted by the
their ISP's service agreement to run mailservers. To use that one, you
can add

 FEATURE(`dnsbl', `dynablock.easynet.nl', `"Access denied to mail host \
 "$&{client_addr}". See http://dynablock.easynet.nl/errors.html"')dnl

to your sendmail.mc (all on one line), and regenerate sendmail.cf.
You can use more than one; these days, it's practically essential to
do so. There's some information on DNSBL's in the base system docs:

  less +/dnsbl /usr/share/sendmail/README

and a little more among the FAQS on sendmail.org.

There's actually quite a few free DNSBL's these days. A good source is

  http://www.openrbl.org

You can enter an IP address of a SPAM source, and they'll display any
lists that that host is on, including a description and evaluation of
the lists, and links to the list's web site.

Frederick