Robert Heller wrote:
If the machine is a public-facing smtp server, I would look first to see if you are getting the problem I was having. Maybe looking at the maillog to see if the volume of incoming mail is just overwhelming the system. In which case you need to do things to keep sendmail from running to many processes, either by throttling the connection rate and/or be using the accessdb to discard or reject connection from known problem networks.
Very simple solution is to implement Reverse DNS check. My Postfix mail server refuses to accept any mail from FQDN without valid reverse DNS. I (was?) also use graylisting and few other measures, but Reverse DNS helped immensely in lowering SPAM that comes to my mailboxes. I would say that reduction is some 70-80%.
Ljubomir