When you're in the Control Panel view, you have leads and blocked. What does Blocked mean?
Blocked means that those are lead that either opted out or have bad email addresses(hard bounces)
View Blocked Leads in a Smart Campaign - Marketo Docs - Product Docs
"Blocked leads are people in the Marketo database that are marked blacklisted, unsubscribed, marketing suspended, and that have invalid/empty email."
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