UNIX for Advanced & Expert Users

It seems that mail from our servers are going through a third party security mail scanner (offsite),
due the the mx records specified on our internal and external DNS servers.
However, our internal user to user email does not go through the third party security mail scanner.

I discovered that our internal user to user email does not go through the third party security scanner because,
it does not need to. Email clients (outlook, eudora, and etc...) are automatically directed to our
email server, which does not require them to go through DNS and look for an
email server through the MX records.

Our Servers in the other hand, go through the third party security mail scanner.
Our servers still needs to look for an email server through DNS (MX).

I have this error messages every time I try to mailx to myself:

# mailx -v -s 'test mail from server' xnightcrawl@mydomain.com < /tmp/testmail.xnightcrawl.log
# mydomain.com: Name server timeout
xnightcrawl@mydomain.com... Transient parse error -- message queued for future delivery
xnightcrawl@mydomain.com... queued

I think this error is telling me that sendmail is having problems resolving with our DNS setup.
However, I quadruple checked our DNS configuration on the server and it looks okay. nslookup is able
to resolve our mail server, dns server, its own name and IP.

The only discrepancy I found was our external DNS. It does not have the server in question entered in
the database file or an "A" record (zone file), but the internal DNS does.

Please forgive me. I'm new to sendmail and email administration. Any suggestions or ideas will truly be appreciated.

This is telling you that there is a problem with DNS.

Check your /etc/resolv.conf on the server that this error happened on. If the server is on your internal network, then it should be resolving to the internal DNS. If it's on an external network, then it could be going to the external DNS or internal DNS (it matters where the server is in relation to the firewalls and the internal network)

You need to verify the following on that server:
You can use nslookup - once you get into nslookup, get the output of the following commands:
Put in the IP of the MX server
>xxx.xxx.xxx.xxx
Check that it comes back with the correct info
Put in the name of the MX server
> my-mx-host
Check that it comes back with the correct info
Put in the following to check PTR record (where xxx.xxx.xxx.xxx is the IP of the MX server
> set type=ptr
> xxx.xxx.xxx.xxx
Check that it comes back with the correct info
Put in the following to check MX record (where mydomain.com is the actual domain of the MX server
> set type=mx
> mydomain.com
Check that it comes back with the correct info

You can also check Sendmail with the following tests
$ /usr/lib/sendmail -d0.1 -bt < /dev/null
Make sure there are no errors in the output
It should look something like this:
Another question - is the email you are sending going to the same domain (mydomain.com)? Or is it being sent to a different domain (and out of your network - yahoo.com)?

And post the OS and version - and the version of Sendmail (especially if it is compiled by you/your company versus the one that came with the system). Same with your DNS.

If the mail is to be sent out to another domain... then what all has to be checked to insure that the mail is sent??