Detecting the Registrar of the sending host?

[Marc Perkel]

Is there an easy way to detect the registrar of a domain through DNS? 
For example - can I easilly figure out if an email I'm processing is 
hosted by GoDaddy or Tucows?

Here's what I'm thinking. I think there's some expensive and highly 
secure registrars out there who are the registrar of expensive domains 
and probably have no spam domains at all. This could be used to create 
white rules.

Can this be done?