Restriction classes provide the last wrinkle in the Postfix anti-spam parameters. They allow you to define a set of restrictions that you can assign to the righthand side of an access table. They cannot be used in header and body checks—only in access tables. Restriction classes let you set up different restrictions for different clients, senders, and recipients. Restriction classes are a powerful tool that can provide great flexibility in Postfix UBE restrictions. If you require any sort of complicated rules to block spam, it is well worth your while to invest the time to understand restriction classes.
Restriction classes are particularly useful when you need to create exceptions to your normal restrictions. To illustrate with an example, let's create two classes of users. One group wants to receive all messages addressed to them whether or not the messages are spam. The other group prefers particularly stringent checks against spam even at the risk of losing some legitimate mail.
We'll call the two classes "spamlover" and "spamhater."
You must list all of the restriction classes you plan to define in the
smtpd_restriction_classes = spamlover, spamhater
We've invented the names of the classes, but once listed with
smtpd_restriction_classes, they can be treated like any other restriction rule. You can assign a list of restrictions to be considered for the class. Once defined, the restriction ...