Basically, what this does is let you put a server (firewall) up so that all incoming mail to your server goes through this first, checking it for spam and viruses, and than sends the mail on to your cPanel server.
It's much better than doing it on the cPanel server, since it's more realiable (better checking.) as well as saves the resources used if you had it on your webserver.
what this does is, after the client issues a RCPT TO:<[email protected]>, the intermediate server calls the main server to check whether the email address exists.
if this check isn't performed, the intermediate server accepts mail to any local part. so, you waste cpu time processing a mail that will eventually be rejected by the main server. besides, the intermediate has to send out a bounce if the main server rejects it.
Very cool..I'll have to play with it, initial tests caused all email to bounce (most likely due to the lack of intelligence in the routers, right now they simply refer to the one file as to where it needs to send the email, it doesn't do dns checks or what not..which could cause issues when trying to verify senders or receivers I believe.