NSLOOKUP is a quick and convenient way to verify that your DK/DKIM records are set up properly. The policy for DK/DKIM is a TXT record at this location:

_adsp._domainkey.<domain.com>

For the selector record you have to use:

<selector>._domainkey.<domain.com>

For example, do a NSLOOKUP for TXT at: c3po._domainkey.altn.com

Open the Start menu
Select Run...
Type cmd [Enter]
In the command window, type: NSLOOKUP [Enter]
Type: set q=txt [Enter]
Type: dcontrol._domainkey.tweenpath.net [Enter]