mail delivery problems / MX record issue?
Kevin Darcy
kcd at daimlerchrysler.com
Wed Jun 6 23:47:18 UTC 2001
nospam at home.com wrote:
> On 5 Jun 2001 14:23:53 -0700, Kevin Darcy <kcd at daimlerchrysler.com>
> wrote:
>
> >At the very least, they should be able to control what domains their mail
> >server accepts mail for. Whether they can give a nicely-tailored rejection
> >message on a per-domain basis, is another matter.
>
> Is it possible for a *NIX mail server not to accept mail for
> particular users?
Well, trivially, yes. If my mail server has no mailbox for user "foo", then I'll
bounce mail sent to that mailbox. Now, if you mean, reject mail for particular
users in *real-time* (i.e. as soon as you get the RCPT TO in the
SMTP conversation), this is often not possible to do because the mail server is
just a relay and doesn't have full knowledge of what mailboxes are valid and what
aren't. Plus, even if it has that knowledge, this validity-checking could be
quite resource-intensive (remember that a given SMTP message can have multiple
RCPT TO's), and it might give spammers an efficient way to test the validity of
their mailing lists. All in all, this feature is of dubious value and I doubt
very many mail server packages implement it "out of the box".
But a) this is really a sendmail question rather than a DNS question (and thus
OT for this list) and b) I thought we were talking about rejecting mail for a
whole *domain*, which is (or its converse -- only accepting mail for specific
domains) a much more commonly-implemented feature, really, a requirement, in
order to avoid being an open relay.
> >I don't know whether MSN's mail software will failover to using MX'es if mail
> >is *rejected* on the A-record host, but I'm fairly confident that it will
> >failover if it can't connect to port 25 on the A-record host, since
> >"chrysler.com" has nothing listening on port 25 and we get plenty of mail
> >from MSN.
>
> Makes sense. Are you in Auburn Hills, btw?
Not today. My "home base" is elsewhere in the Detroit metro area.
- Kevin
> >Really, you should interrogate your hosting company as to why they don't make
> >a clean separation between web and mail services. Mixing them together like
> >this just encourages brokenness like MSN's.
>
> I'll see what I can do. Thanks.
>
> >
> >- Kevin
> >
> >nospam at home.com wrote:
> >
> >> The web server is an offsite machine, hosting probably dozens of
> >> web sites and is something I don't have any control over.
> >> If there's anything I can ask them (hostway.com) to do that wouldn't
> >> affect their other users, please let me know.
> >> The other thought I had was to point the top-level domain to our mail
> >> server and only assign www.epcom.com to the web server. But then
> >> that would prevent people from accessing the web page via
> >> http://epcom.com/.
> >>
> >> Thanks.
> >>
> >> On 4 Jun 2001 15:12:29 -0700, Kevin Darcy <kcd at daimlerchrysler.com>
> >> wrote:
> >> >Why is the web server accepting mail in the first place?!? If it's
> >> >listening on the SMTP port at all, it should be emitting "use MX records,
> >> >bozo!" in its SMTP banner and immediately disconnecting.
> >> >
> >> >Geez, I thought all Internet mailers fixed this problem *eons* ago. Then
> >> >again, we're talking MSN here...
> >> >
> >> >
> >> >- Kevin
> >> >
> >> >nospam at home.com wrote:
> >> >
> >> >> Hello.
> >> >>
> >> >> I'm a DNS newbie for the most part yet I'm responsible for maintaining
> >> >> a small business set up. The situation I have is this:
> >> >>
> >> >> - Domain web server is hosted by an ISP
> >> >> - Domain MX record and mail is sent to an internal Linux mail server
> >> >> - Backup MX record sends mail to a different ISP in case our server is
> >> >> down
> >> >>
> >> >> The situation I have is that some mail shows up on the web server and
> >> >> is not routed to the mail server. 95% of this mail is spam, however,
> >> >> some legitimate messages are being sent there. I think maybe I'm
> >> >> running into this issue
> >> >> http://www.acmebw.com/askmrdns/archive.php?category=88&question=574
> >> >> because the legitimate mail all seems to be coming from msn.com.
> >> >>
> >> >> Is there anything I can do about this? Here's the output of dig for
> >> >> the domain:
> >> >>
> >> >> ;; ANSWER SECTION:
> >> >> epcom.com. 16h8m3s IN NS AUTH00.NS.UU.NET.
> >> >> epcom.com. 16h8m3s IN NS AUTH61.NS.UU.NET.
> >> >> epcom.com. 1h41m36s IN A 64.41.85.9
> >> >> epcom.com. 5h10m1s IN MX 10 saturn.epcom.com.
> >> >> epcom.com. 5h10m1s IN MX 100 mail.UU.NET.
> >> >> epcom.com. 5h15m12s IN SOA AUTH00.NS.UU.NET.
> >> >> hostmaster.UU.NET. (
> >> >> 990519 ; serial
> >> >> 6H ; refresh
> >> >> 1H ; retry
> >> >> 2w6d ; expiry
> >> >> 6H ) ; minimum
> >> >>
> >> >> ;; AUTHORITY SECTION:
> >> >> epcom.com. 16h8m3s IN NS AUTH00.NS.UU.NET.
> >> >> epcom.com. 16h8m3s IN NS AUTH61.NS.UU.NET.
> >> >>
> >> >> ;; ADDITIONAL SECTION:
> >> >> AUTH00.NS.UU.NET. 17h36m34s IN A 198.6.1.65
> >> >> AUTH61.NS.UU.NET. 38m5s IN A 198.6.1.182
> >> >> saturn.epcom.com. 1h41m36s IN A 63.69.1.34
> >> >> mail.UU.NET. 1m17s IN A 199.171.54.106
> >> >> mail.UU.NET. 1m17s IN A 199.171.54.122
> >> >> mail.UU.NET. 1m17s IN A 199.171.54.245
> >> >> mail.UU.NET. 1m17s IN A 199.171.54.246
> >> >> mail.UU.NET. 1m17s IN A 199.171.54.98
> >> >>
> >> >> Here's the header for one of the misdelivered messages:
> >> >>
> >> >> >From DELETED at email.msn.com Sun Jun 3 13:23:27 2001
> >> >> Return-Path: <DELETED at email.msn.com>
> >> >> Received: from cpimssmtpu13.email.msn.com (cpimssmtpu13.email.msn.com
> >> >> [207.46.18
> >> >> 1.88])
> >> >> by coolio.siteprotect.com (8.9.3/8.9.3) with ESMTP id NAA05631
> >> >> for <resume at epcom.com>; Sun, 3 Jun 2001 13:23:26 -0500
> >> >> Received: from oemcomputer ([63.27.42.144]) by
> >> >> cpimssmtpu13.email.msn.com with Microsoft SMTPSVC(5.0.2195.3225);
> >> >> Sun, 3 Jun 2001 11:23:01 -0700
> >> >> Message-ID: <008301c0ec5a$0d10f200$902a1b3f at oemcomputer>
> >> >> From: "DELETED" <DELETED at email.msn.com>
> >> >> To: <resume at epcom.com>
> >> >> Subject: Employment
> >> >> Date: Sun, 3 Jun 2001 14:07:18 -0400
> >> >> X-Priority: 3
> >> >> X-MSMail-Priority: Normal
> >> >> X-Mailer: Microsoft Outlook Express 5.00.3018.1300
> >> >> X-MimeOLE: Produced By Microsoft MimeOLE V5.00.3018.1300
> >> >>
> >> >> Many thanks.
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