Host unknown (Name server: domain.com: no data known)

[Khalid J. Hosein]

Hello,

I'm having an interesting problem with sendmail:

When a user (running either Netscape Messenger or Eudora as their mail
client) receives an e-mail from us...@domain.com and hit Reply, the mail
bounces with the message as below.

----- The following addresses had permanent fatal errors -----
<us...@domain.com>

----- Transcript of session follows -----
550 <us...@domain.com>... Host unknown (Name server: domain.com: no data
known)

However, if the user addresses the us...@domain.com directly, as in "To:
us...@domain.com" and sends it off, it goes just fine. I can verify this
in the syslog for sendmail, where it gives a stat=Sent (OK).

It seems like sendmail is using DNS MX lookups just fine on outgoing
To:, but sometimes fails when the user does a Reply. (Oh, the From: and
Reply-to: addresses in the original e-mails match.) That's the other
wierd thing - it doesn't fail for every domain.com, just a few here and
there.

Thanks in advance for any help!

_Khalid

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=================================================
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the Motion Picture'.

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[Ashley Drees]

I too am seeing mail failing with this error.

It seems to only happen to a couple of domains... and if i run nslookup
I cannot see what is wrong... if you get any pointers on this.. please
let me know.

A

[Claus Assmann]

use sendmail itself:

echo '/mx domain.that.fails' | sendmail -bt
echo '/map host domain.that.fails' | sendmail -bt

If those don't work, then you maybe disabled DNS for sendmail.
Add a debug switch, e.g., -d8.8 to see more details.
--
If you feel the urgent wish to send me a courtesy copy of a Usenet
posting, then make sure it's recognizable as such!
The FAQ: http://www.sendmail.org/faq/ Before you ask.

[Ashley Drees]

Thanks.. pointer taken...

/etc/mail/service.switch was the problem.. only had files under
hosts.... added dns and all problems went away... feel so dumb...

[Khalid J. Hosein]

My problem isn't global. It only occurs for 1 or 2 messages per day on a
500 message per day system. The other strange thing is that messages
that fail once or multiple times, may go through if a user tries to send
them again. I've turned on debugging switches -d8.1 and -d8.8, but have
not seen any reporting from them as yet.

DNS is enabled for sendmail, and the service switch (nsswitch.conf for
me) has it turned on as well. resolv.conf uses the same
machine for name resolution since it's also running our main
name server. Performing straight nslookup's or dig's on the system are
successful.

The workaround at this point is just to have the users re-try their
e-mails until they don't bounce any more. But that's not a real
solution!

In article <8nbh6p$gar$1...@zardoc.endmail.org>,
Claus Assmann

<ca+sendmail(-no-copies-please)@mine.informatik.uni-kiel.de> wrote:
>
> use sendmail itself:
>
> echo '/mx domain.that.fails' | sendmail -bt
> echo '/map host domain.that.fails' | sendmail -bt
>
> If those don't work, then you maybe disabled DNS for sendmail.
> Add a debug switch, e.g., -d8.8 to see more details.
> --
> If you feel the urgent wish to send me a courtesy copy of a Usenet
> posting, then make sure it's recognizable as such!
> The FAQ: http://www.sendmail.org/faq/ Before you ask.
>

[Claus Assmann]

Khalid J. Hosein wrote:

> My problem isn't global. It only occurs for 1 or 2 messages per day on a
> 500 message per day system. The other strange thing is that messages
> that fail once or multiple times, may go through if a user tries to send
> them again. I've turned on debugging switches -d8.1 and -d8.8, but have
> not seen any reporting from them as yet.

Sometimes DNS servers are misconfigured and give wrong answers.
If such an answer is non-temporary (i.e., not TEMPFAIL) then
sendmail must bounce the message.

So I would assume that there is some DNS problem, which is
outside the scope of sendmail. It's very hard to diagnose
such occacional problems :-(

[led...@my-deja.com]

I have a similar problem. Intermittently fails
with "Host unknown". Next time it works. Used
the -bt mode of testing sendmail and the host was
found every time. Entered the host in
the /etc/hosts file and it still fails. The key
question, I believe, is why it would be
intermittent.

In article <8nsrnv$bbr$1...@zardoc.endmail.org>,
Claus Assmann <ca+sendmail(-no-copies-please)

Sent via Deja.com http://www.deja.com/
Before you buy.