KB00022808 How does Mail Barring work?

Barring is done with a Type 2 Wildcard List.  The contents of the barring lists are used to identify addresses that will be rejected.

The list is read top to bottom.  Each entry alters the barring by including or excluding a range of addresses (to reject). To include an address range, enter a wildcard specification (which may or may not actually include wildcard characters).

To exclude an address range, enter a wildcard specification preceded by a tilde (~).

There are four wildcard characters in a Type 2 Wildcard:

* One or More characters
? One character
$ One alphabetic character (A-Z, any case)
% One numeric character (0-9)

Example (Sender Barring)

*@*%%%%*
*@%%%%*
*@*%%%%
%%%%*@*
*@netcom.com
*@hotmail.com
~myfriend@netcom.com
~myfriend@hotmail.com
spammer@spam.net

Description of the examples

Excludes any address with four sequential numbers in the domain part.
Excludes any address beginning with four sequential numbers.
Excludes anything from NetCom and HotMail, except for myfriend@netcom.com and myfriend@hotmail.com.
Excludes the specific address spammer@spam.net.

Note:

Barring is only effective on the sender and recipient addresses. This is because the barring is designed to take place during the SMTP transaction -- i.e. before download even begins.

Messages stored in Mailtraq will show the sender field in the Return-Path: header.