how to prevent sendmail forwarding for relays without PTR

[Ome Ko]

I'm receiving mail from a server without a PTR record for an emailaddress that is forwarded in aliases to a gmail account. In the maillog it says it's deferred, but actually the mail is forwarded as is to our friends of the alphabet holding.
I put the IP address of this rogue server in access in order to get it discarded, but I'm still getting angry postmaster messages from beforementioned friends that the relay has no PTR record of which I'm painfully aware.

Is there a way to explain to sendmail not to forward deferred mail?

 

[Ome Ko]

For future reference: hacksolved by adding a sendmail denial line to /etc/hosts.allow