Spam rule for HTTP/HTTPS request to sender's root domain

[Mike Marynowski]

Hi everyone,

I haven't been able to find any existing spam rules or checks that do 
this, but from my analysis of ham/spam I'm getting I think this would be 
a really great addition. Almost all of the spam emails that are coming 
through do not have a working website at the room domain of the sender. 
Of the 100 last legitimate email domains that have sent me mail, 100% of 
them have working websites at the root domain.

As far as I can tell there isn't currently a way to build a rule that 
does this and a Perl plugin would have to be created. Is this an 
accurate assessment? Can you recommend some good resources for building 
a SpamAssassin plugin if this is the case?

Thanks!