You may define rules that will accept or reject email from certain senders or domains of the envelope sender. These rules are evaluated by most specific match. Once a Rule is matched, no further rules are evaluated. It is important to consider the order of evaluation when creating rules.
The envelope sender is searched in this order:
user@sub.example.com
@sub.example.com
@.sub.example.com
@.example.com
@.com
@.
Example: Deny all email from example.org except for email sent by Bob (2 rules):
(Rule 1) Sender: bob@example.org, Policy: Whitelist
(Rule 2) Sender: @example.org, Policy: Blacklist
To deny all email from a specific domain and any subdomains of that domain:
Sender: @.example.com, Policy: Blacklist