Ban Internal E-Mails Just Because There's A Lot Of Spam?
Who manages the spam filters?
Or how about this: Brush off the entire mail server, setup a mail server from scratch, don't allow outgoing mail through SMTP, block ports in the firewall for receiving mail from the outside, and there you have it -- a private e-mail server that allows employees to send and receive e-mails to and from each other. If you want to allow sending/receiving e-mails from anyone outside your network, setup a SpamAssassian spam filter to only allow e-mail messages you want to receive from.
That's it. Simple as that. -- Current Soft Phone (temp): Ekiga (ordered Yealink T22P to switch from Ekiga) Phone System: Asterisk 1.8; Server: Ubuntu Server 10.04 with Windows Server 2008 R2 Standard as guest