Sub-dividing 'non-spam'

I realize that the main function of SA is to separate spam from 
non-spam.  But I am encountering a growing need to sub-divide some 
non-spam mail between important (keep) specific mail related to a 
purchase vs. promotional mail from the same vendor.  For example, we do 
a lot of RVing.  We make reservations sometimes months ahead at a 
campsite and receive confirmation emails, etc.  But we also like to hear 
about other promotions and offers from the same camp site.  I want to 
expire and autodelete promotions-only email after a certain expiry 
period while permanently keeping reservation confirmations/receipts.  It 
would be wonderful if these emails came from 
"[email protected]" and "[email protected]".  But 
that would be too easy, and rarely occurs.  Mostly everything comes from 
info@... or some other common email.

I suspect this is a total long-shot.  But just curious if there are any 
tricks/techniques that others are using that can somewhat definitively 
separate reservation confirmations from promotions/marketing email so I 
can categorize lifecycle accordingly?  I suspect there may be some 
training per vendor. But what is the best/recommended service to be 
trained?   Any suggestions welcome.

Thx

Jerry