I was wondering if anyone here knows the best way to stop / blacklist domains for users on the mail server? I am being told that nobody on my company email server is permitted to send email from our mail server to aol.com, gmail.com, hotmail.com, msn.com, & yahoo.com. I was wondering what is the best practice method in Postfix to prevent all mail users to send email to these domains. Is this possible? Thanks for any info!