To unjoin or remove a domain from the Domain List
On the Domains page, select the domain from the list and click Unjoin or Delete.
A confirmation dialogue displays. Confirm that you want to remove the domain from the list.
Warning:
When a domain is removed, it is also removed from any authentication rules that specify it.
If it is the only domain specified in a rule, when the domain is removed the rule is made invalid and, therefore, the rule is removed.