any email with a FROM as coming from our domain but is not a user (left of @ sign)
You might be able to get your MTA to check that, the same as it does for recipients. You know what addresses are valid @ your own domain, so it's reasonable to refuse mail from any others. We have sendmail doing this during check_mail. It stops 2% of our incoming. You use postfix and I am not familiar with how it might be done with that. Joseph Brennan Lead Email Systems Engineer Columbia University Information Technology
