Please note, when adding SPF checking/enforcing for a domain or email address, you will want to first confirm that the domain has a valid and up to date SPF record. If there is no SPF record, or the SPF does not define the correct sending IP addresses, then Impersonation Protection could cause legitimate messages to be sent to the quarantine (if that option is selected).
SPF checking is not enforced by default. To take advantage of the SPF checking on our system, there are 2 steps: