With the Incoming Mail Filters you can set-up global rules for filtering incoming emails. These rules are applied on every incoming mails on all Mail Accounts.
Sender email address filters
On the Sender email address filters page you can create a ruleset to accept or reject the emails based on the sender email address.
A rule consists of a regular expression and an action. When an email comes in, the engine checkes the first rule if it's regular expression matches the sender's email address. If it matches the expression, then the selected action for the rule is applied. If it does not match, then the next rule is checked. If there is no match, then the default action is applied.
You can create any number of Rules and the order of the rules can be changed by dragging and dropping the rules using the arrows icon in the first column.
Obviously the default action cannot be deleted and cannot be moved.