Since the Robtex.com redesign, which does not seem to work properly under some IE versions, we had to use other resources or say find them. Beside mxtoolbox.com we use for MX SPAM lookup there is dnsinspect.com which is really nice and does most of the stuff for you automatic incl. good Name server check.
http://www.dnsinspect.com/ntfaq.ch
https://toolbox.googleapps.com/apps/checkmx/