Date: Fri, 12 Sep 1997 16:01:19 -0500 From: Jonathan Lemon <jlemon@americantv.com> To: Dave Babler <dbabler@Rigel.orionsys.com> Cc: Dan Busarow <dan@dpcsys.com>, freebsd-questions@FreeBSD.ORG Subject: Re: Help with Sendmail/DNS Message-ID: <19970912160119.32472@right.PCS> In-Reply-To: <Pine.BSI.3.95.970912115807.24547A-100000@Rigel.orionsys.com>; from Dave Babler on Sep 09, 1997 at 12:02:17PM -0700 References: <19970911194023.47189@right.PCS> <Pine.BSI.3.95.970912115807.24547A-100000@Rigel.orionsys.com>
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On Sep 09, 1997 at 12:02:17PM -0700, Dave Babler wrote:
> On Thu, 11 Sep 1997, Jonathan Lemon wrote:
> > On Sep 09, 1997 at 04:18:55PM -0700, Dave Babler wrote:
> > > It looks like I'm hosed then, host altair is just for testing. The REAL
> > > desired operation is:
> > >
> > > mail to orionsys.com -> rigel -> bbs.orionsys.com
> > > mail to bbs.orionsys.com -> rigel -> bbs.orionsys.com
> > > mail to rigel.orionsys.com -> rigel
> > > mail to altair.orionsys.com -> rigel -> altair...
> > >
> >
> > What about trying ``O TryNullMXList'' (or ``Ow'' for older sendmails) in
> > the sendmail.cf file on rigel?
> >
> This does seem to work, curing the looping MX problem... except that
> according to the Sendmail Reference, "The TryNullMXList (w) option is not
> safe as of V8.8.4." Also, there doesn't seem to be an m4 macro to invoke
> it, which tends to indicate to me it isn't 'approved' any more for some
> reason... does anyone know why?
>From the sendmail README:
SECURITY: the TryNullMXList (w) option should not be safe -- if it
is, it is possible to do a denial-of-service attack on
MX hosts that rely on the use of the null MX list.
Also, you can configure it with M4:
define(`confTRY_NULL_MX_LIST', `True')dnl
It's true that this approach has been 'deprecated' ever since it was
introduced in v8.4.
An alternative approach would be to define a separate mailer, which
has the ``0'' flag set in it's Flags list, which says to send direcly,
without doing a MX lookup:
Add new F=0 (zero) mailer flag to turn off MX lookups.
Then pass off all mail destined to {bbs|altair} to this mailer.
--
Jonathan
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