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DNS lookups from Sendmail

David Crowe
Advisor

DNS lookups from Sendmail

I am having some problems with sendmail when it is looking up DNS for mail delivery or to resolve an MX record on inbound email. When we captured the network traffic, it was determined that sendmail is doing a request for all records whenever it is resolving a domain name. I would have expected that it would only be looking up an MX record. Is that normal? Can this be changed?
13 REPLIES
Charles McCary
Valued Contributor

Re: DNS lookups from Sendmail

What does a cat of your nsswitch.conf file show?
someone_4
Honored Contributor

Re: DNS lookups from Sendmail

what happends if you do
nslookup domain.com

Richard
David Crowe
Advisor

Re: DNS lookups from Sendmail

I do not have a nsswitch.conf on this server. DNS is not located on the same server as sendmail. Do I need to have this configuration if DNS is not on this server?

What are you expecting to see when I do an nslookup? If I don't set any type, I appear to get a number of A records for the domain that I queried.
Charles McCary
Valued Contributor

Re: DNS lookups from Sendmail

Your problem description stated that you are using DNS. If you are using DNS, then you need an nsswitch.conf file in order to figure out how to resolve each DNS name. Also, you need a resolv.conf file that lists your DNS servers.

tx,

C
David Crowe
Advisor

Re: DNS lookups from Sendmail

I have configured DNS using the set_parms addl_netwrk command. Does this not set up this server to use the specified DNS? Does Sendmail not use this configuration?
someone_4
Honored Contributor

Re: DNS lookups from Sendmail

Nsswitch can be found in /usr/newconfig/

# ls -l /usr/newconfig/etc/nsswitch*
and copy it over.

Richard
David Crowe
Advisor

Re: DNS lookups from Sendmail

When I looked in the directory that you stated, there is no nssswitch.conf file. If the nsswitch.conf file is missing, doesn't it use a default configuration? Would this not be adequate or does it need hard coded information?
Dave Kelly_1
Respected Contributor

Re: DNS lookups from Sendmail

You should have the following entry in your /etc/nsswitch.conf file:


hosts: dns [NOTFOUND=continue UNAVAIL=continue] files

Make sure that /etc/resolv.conf contains your nameserver details otherwise sendmail will assume that you are trying to resolve names using the local machine.
David Crowe
Advisor

Re: DNS lookups from Sendmail

I created the nsswitch.conf from the nsswitch.hp_defaults file and I verified the entries in resolv.conf. Now whenever I try to clear the queue (Sendmail -q -v)I get an "NIS map mail.aliases specified but NIS not running" message. It still seems to run the command but I get this message. How do I get rid of this message and do I need any of the entries in nsswitch.conf other than the hosts: DNS entry.
someone_4
Honored Contributor

Re: DNS lookups from Sendmail

what about when you do
sendmail -v user@domain.com
this is a test
.

what is the output?
and where does the mail die ?

Richard
David Crowe
Advisor

Re: DNS lookups from Sendmail

I'm sorry, I guess I didn't make myself clear. Mail is flowing. There is no real problem other than what we saw in the network capture. Instead of seeing a request for MX information for each domain name, we are seeing a request for all records. In most cases the name is resolved and the mail is sent.
Satish Y
Trusted Contributor

Re: DNS lookups from Sendmail

As a last trial, is ur all MX records appended by ".", If not u must do it.

Cheers...
Satish.
Difference between good and the best is only a little effort
Thom Cornwell
Frequent Advisor

Re: DNS lookups from Sendmail

It would appear from the NIS message that the default file has something like "files dns nis" as a means of determining host names