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Home > Archive > IIS and SMTP > January 2008 > Some problems with IIS 5 on w2k - dns error
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Some problems with IIS 5 on w2k - dns error
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| Ralph A. Schmid, dk5ras 2008-01-03, 7:30 am |
| Hi,
I have some strange effects with a smtp server of the IIS 5 sort, on a
w2k server system, behind a NAT. It should take the emails and deliver
them to a smarthost, but in most times this fails, the mail keeps in
the queue, and the eventlog tells me (when sending an email for
example to ras@invalid.invalid):
"Message delivery to the remote domain invalid.invalid failed for the
following reason: An internal DNS error caused a failure to find the
remote server"
Data (words): 0xc00402e7
Sometimes for no obvious reason it works.
The server is configured to try no direct delivery, so why does it
want to resolve the receivers domain name, when it should use an
external smarthost?!
Internet connectivity works on the server without any problems.
Nslookup on this machine gives the expected results.
So do I miss something? Some setting? Any additional services
necessary, that I did not set up, or what else am I doing wrong?
Any help is highly appreciated!
Ralph.
http://www.dk5ras.de/
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| Sanford Whiteman 2008-01-03, 1:22 pm |
| > The server is configured to try no direct delivery, so why does it
> want to resolve the receivers domain name, when it should use an
> external smarthost?!
Is your smarthost entered using a square-bracketed IP, i.e. [1.2.3.4] ?
--Sandy
------------------------------------
Sanford Whiteman, Chief Technologist
Broadleaf Systems, a division of
Cypress Integrated Systems, Inc.
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| Ralph A. Schmid, dk5ras 2008-01-04, 7:37 am |
| "Sanford Whiteman" <swhitemanlistens-software@cypressintegrated.com>
wrote:
>Is your smarthost entered using a square-bracketed IP, i.e. [1.2.3.4] ?
No, it uses a domain name that is resolved. At the moment (after
installing the DNS server) it works; but why does it need a DNS on the
local machine, and not simply use the supplied DNS?
Ralph.
http://www.dk5ras.de/
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| Sanford Whiteman 2008-01-04, 1:27 pm |
| > No, it uses a domain name that is resolved. At the moment (after
> installing the DNS server) it works; but why does it need a DNS on
> the local machine, and not simply use the supplied DNS?
[The error that you're seeing refers to the smarthost's A record,
BTW.]
A typical and stable config certainly does not _need_ to have a local
DNS server: lookup of the smarthost's A record can happen over the
wire. You can also use a HOSTS entry or the square-bracketed IP
(though these options mean that you will not be aware of IP changes
from your smarthosting provider).
However, using a remote DNS server across your WAN link -- if that's
what you're doing -- does mean that you are reinjecting latency and
overhead into a setup which is designed to take load _off_ your box.
Depending on your daily mail traffic and client DNS cache, you could
be sending quite a bit of surplus traffic over the wire. In and of
itself, a constant stream of DNS traffic won't cause any problems; but
an increased load means that line errors, firewall/router UDP
processing errors, remote DNS server quotas and stability, etc. will
be more likely to affect you. I don't know which provider's doing your
smarthosting and/or DNS, but I only use smarthosting if forced and
never rely on an ISP's DNS server over my own.
Even if your DNS server was formerly on a different box on your LAN
(rather than across the WAN), same theory holds. SMTP server is using
the same DNS lookups, just against a box that it can reach without
error. You can't trust one-off NSLOOKUPs to tell you how dirty the
connection is; need a sniffer trace for that.
--Sandy
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Sanford Whiteman, Chief Technologist
Broadleaf Systems, a division of
Cypress Integrated Systems, Inc.
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