Which policy cannot apply the HOLD action on messages?

The HOLD action is designed to temporarily retain messages within the email gateway until further inspection or action can be taken. Among the options presented, the policy regarding Blocked Senders is focused on outright rejecting or blocking messages from specified addresses without the need for further analysis.

In practice, the Blocked Senders policy operates by identifying emails from predetermined addresses that are considered undesirable and preventing their delivery. This is fundamentally different from the content review processes involved in policies like Suspicious Attachments, where there might be a need to hold content for a detailed examination, or Content Filters that analyze message content for compliance or threats.

On the other hand, Sender Verification typically involves validating whether a sender's address is legitimate or spoofed but does not inherently involve holding messages like the other policies could. Thus, in the context of the HOLD action application, Blocked Senders is the policy that cannot utilize this function since its purpose is to block rather than to evaluate.