I guess you are on right track...see this for setting up zone at DNS server using wildcard
this way you get all incoming requests for
company2.emailjobs.com and so on to a specific website created on IIS - make sure you dont have host header with website name and only with IP address.
And use IIS redirect or MVC or traditional web form to intercept request at code level and serve request...
Saurin Travadi, Apr 21, 2011