Sendmail does DNS lookup

Sendmail does DNS lookup

Post by Ian Rawling » Sun, 18 May 1997 04:00:00



Hello all, whenever I send some email, sendmail kicks off diald,
presumably to verify the address I'm sending the email to. I'm running
sendmail in queue-only mode, so it doesn't actually send the mail, but
this initial dialling up is annoying!

Does anyone know how to stop it? I've looked through all the sendmail
information I can find, and it seems that the best way would be to
prevent sendmail from doing DNS lookups at all, but I don't really want
to do this as the relay host has four IP addresses associated with it,
and one is picked when I run the mail queue.

I've also tried adding the relay host to my hosts file so DNS is not
required to find it. This was to test if it was looking up the relay
host's email address, but my blasted slakware release doesn't have the
source for sendmail, only binaries. I've now downloaded the source, but
am missing the ndbm.h so can't currently compile it. I'll get this at
some point soon, but am not hopeful that there'll be any change.

Hmmm, it even dials out when I send to a local address... This needs
further looking into..

Can anyone help out on what I've found so far?

--

There are no facts, only opinions

 
 
 

Sendmail does DNS lookup

Post by Ian Rawling » Sun, 18 May 1997 04:00:00



> Hello all, whenever I send some email, sendmail kicks off diald,
> presumably to verify the address I'm sending the email to. I'm running
> sendmail in queue-only mode, so it doesn't actually send the mail, but
> this initial dialling up is annoying!

I've now managed to stop this (by reading the diald FAQ - I managed to
miss this!) but now when I do a mailq to see what's waiting to go out,
it dials!

--

There are no facts, only opinions

 
 
 

Sendmail does DNS lookup

Post by Ian Rawling » Mon, 19 May 1997 04:00:00




>> Hello all, whenever I send some email, sendmail kicks off diald,

> I've now managed to stop this (by reading the diald FAQ - I managed to
> miss this!) but now when I do a mailq to see what's waiting to go out,
> it dials!

It's definately doing DNS lookups, and if I block the link, I get the
following error in my syslog;

unable to qualify my own domain name (tarcus) -- using short name

Can anyone help out on this one? My hosts file contains;

127.0.0.1       localhost loghost
194.222.198.188 tarcus

--

There are no facts, only opinions

 
 
 

Sendmail does DNS lookup

Post by Henrik Storn » Tue, 20 May 1997 04:00:00




>> Hello all, whenever I send some email, sendmail kicks off diald,
>> presumably to verify the address I'm sending the email to. I'm running
>> sendmail in queue-only mode, so it doesn't actually send the mail, but
>> this initial dialling up is annoying!
>I've now managed to stop this (by reading the diald FAQ - I managed to
>miss this!) but now when I do a mailq to see what's waiting to go out,
>it dials!

What you want to do is probably to turn off sendmail's DNS lookups
entirely. This can be done by reconfiguring sendmail - add the line
   FEATURE(nodns)
to the .mc file and regenerate sendmail.cf

--

"The POP3 server service depends on the SMTP server service, which
 failed to start because of the following error:
 The operation completed successfully." -Windows NT Server v3.51

 
 
 

Sendmail does DNS lookup

Post by Jon Myat » Tue, 20 May 1997 04:00:00


Build a new sendmail.cf and use the nodns feature in your m4 file.

Jon.

Quote:> It's definately doing DNS lookups, and if I block the link, I get the
> following error in my syslog;

 
 
 

Sendmail does DNS lookup

Post by Ian Rawling » Tue, 20 May 1997 04:00:00



> Build a new sendmail.cf and use the nodns feature in your m4 file.

> Jon.

>> It's definately doing DNS lookups, and if I block the link, I get the
>> following error in my syslog;

Hello Jon,

I thought of that, but I don't want DNS disabled. It's not looking up
details of external machines, it's looking up details that it should be
able to get locally. I've just noticed that INND is also doing it during
a news expire. I'll be looking into this as well.

--

There are no facts, only opinions

 
 
 

Sendmail does DNS lookup

Post by John Phillip » Tue, 20 May 1997 04:00:00



>It's definately doing DNS lookups, and if I block the link, I get the
>following error in my syslog;

>unable to qualify my own domain name (tarcus) -- using short name

>Can anyone help out on this one? My hosts file contains;

>127.0.0.1       localhost loghost
>194.222.198.188 tarcus

That should be:

127.0.0.1       localhost loghost
194.222.198.188 tarcus.demon.co.uk      tarcus

The first name after the IP address is the fully qualified domain name
and after that come the aliases.  I suspect sendmail knows that tarcus
is a nickname and is trying to get the canonical name from a name server
since it isn't available from the /etc/hosts file.  However, I'm no
expert on sendmail.  
--

 
 
 

Sendmail does DNS lookup

Post by Ian Rawling » Thu, 22 May 1997 04:00:00


[chopped to bits for brevity]



>>Can anyone help out on this one? My hosts file contains;

>>127.0.0.1       localhost loghost
>>194.222.198.188 tarcus

> That should be:

> 127.0.0.1       localhost loghost
> 194.222.198.188 tarcus.demon.co.uk      tarcus

> The first name after the IP address is the fully qualified domain name
> and after that come the aliases.
> However, I'm no
> expert on sendmail.

Aaargh! I'm sure I tried that! Basically you've cracked it, thanks a
lot. I think I must have tried the FQDN after the short name, but not
the other way around.

Thanks very much indeed! Now I can say that diald and linux are truly
the dogs you-know-whats. All I need to do is to get around to tuning the
diald filters, and I'll be able to leave my comms setup alone
completely.

--

There are no facts, only opinions

 
 
 

1. Disabling DNS lookup by sendmail in Solaris and suggestion for hardening tools

Is there anybody knows how I can disable dns lookup on sending email by
sendmail?
I know that Solaris does not use /etc/mail/service.switch and I tried to add
the following option
O ResolverOptions=-DNSRCH
in /etc/sendmail.cf
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jass from Sun Microsystems. But I would like to try more hardening tools,
any suggestion? Thank you very much!

Brgds,
Henry

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