Sendmail and reverse DNS check

How do you enable this feature in sendmail? I've looked but can't seem to find it. We're getting a lot of spam from infected machines. Some of these machines don't have reverse DNS entries. An easy way to stop some spam would be to check to see if the relay has a reverse DNS entry. Is this enabled

Re: Sendmail and reverse DNS check

Such a feature doesn't come with sendmail 8, however, it is available from others: http://www.cs.niu.edu/~rickert/cf/ require_rdns is the one you are looking for.