Spam Domino

Are you talking about preventing spam mail from hitting your server from outside, or preventing your users from spamming from inside out? Or internal spam, where a user decides to send their innane emails to everyone on the address list? There is noeasy answer for any of these. You can contract with a service to block incoming mail from known spam sites, but new sites get created daily. Any filtering you do will slow down the mail, and preventing your internal users from sending mail to multiple users is counter-productive. You need to focus this question toward what types of spam are causing you problems, and then ask for strategies that will help mitigate the problems without adding too many more. If your question is about internal users, the best response I can think of is to formulate a good email policy explaining the appropriate use of email, and then enforce your policy.

Type in your domain name 'abc.com' in the 'Allow messages from external internet domains to be sent only to the following internet domains: '

Open the Configuration document for your SMTP server, click Router/SMTP -> Restrictions and Controls -> SMTP Inbound COntrols.

Should do the trick.

Hope this helps