I have a stock install of Postfix from my Ubuntu repository.

When I get spam coming consistently from a certain ISP, I block its IP range. I would rather not do this, but technical people under WHOIS don't take action against my complaints.

I am wondering if there is a way to configure Postfix to do a MX lookup on the sender during the MTA transaction, to match the sending SMTP's server IP address against the one MX record for the mail thats coming from?

Sender (a@example.com) > My Server
My Server > MX lookup example.com
If MX for example.com contains, accept mail, else reject.