The correct answers are B. SMTP verification , C. LDAP verification , and D. User Repository verification . In the Threat Protection Administrator course, Recipient Verification is presented as a feature used to validate whether recipient mailboxes exist before accepting mail for them. The public course guide excerpt confirms that Proofpoint supports using an imported user repository in place of repeatedly querying LDAP, which directly supports User Repository verification as one of the built-in methods. It also places Recipient Verification alongside LDAP-based identity workflows, which supports LDAP verification as a default verification method.

SMTP verification is the remaining standard mailbox-existence check in this feature set and fits Proofpoint’s connection-level validation approach. By contrast, Email the recipient is not a real-time verification method used for SMTP-time recipient validation, CSV file verification is not presented as one of the default Recipient Verification methods in the Proofpoint course materials, and DNS verification checks domain routing information rather than whether a mailbox for a specific recipient exists. In administrator practice, these three methods cover live directory validation, local imported identity validation, and SMTP recipient validation against the destination system. Therefore, the correct three default methods are SMTP verification, LDAP verification, and User Repository verification .