Im runnning Ensim-pro RHE5 - I only have 5 sites on the box and I am not using any email accounts - the server is getting a ton of junk spam and its all being processed by Mailscanner which is using up all the processor cycles

I have some sites on there that send out email via scripts (membership activation emails for new user signups) other than that there is no email being used on the site. I blackholed all the catch-alls but there is still a bunch of junk being processed in the maillog

can I block a port with the firewall - or tell sendmail to ignore all email coming from outside the local host? It shouldn't be receiving any mail at all on that machine - i have other dedicated mail servers.

How can I get my box to only send out mail from my local scripts and ignore (block) all incoming mail

If anyone can help me out i would appreciate it, been looking through google but cant seem to find any answers.