From owner-freebsd-questions Fri Sep 12 14:02:07 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id OAA08661 for questions-outgoing; Fri, 12 Sep 1997 14:02:07 -0700 (PDT) Received: from sumatra.americantv.com (sumatra.americantv.com [207.170.17.37]) by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id OAA08655 for ; Fri, 12 Sep 1997 14:02:04 -0700 (PDT) Received: from right.PCS (right.PCS [148.105.10.31]) by sumatra.americantv.com (8.8.5/8.8.5) with ESMTP id QAA15131; Fri, 12 Sep 1997 16:01:51 -0500 (CDT) Received: (from jlemon@localhost) by right.PCS (8.6.13/8.6.4) id QAA17940; Fri, 12 Sep 1997 16:01:20 -0500 Message-ID: <19970912160119.32472@right.PCS> Date: Fri, 12 Sep 1997 16:01:19 -0500 From: Jonathan Lemon To: Dave Babler Cc: Dan Busarow , freebsd-questions@FreeBSD.ORG Subject: Re: Help with Sendmail/DNS References: <19970911194023.47189@right.PCS> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.61.1 In-Reply-To: ; from Dave Babler on Sep 09, 1997 at 12:02:17PM -0700 Sender: owner-freebsd-questions@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk 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