How can I verify if a person’s electronic mail exists within the database

When making a registration and saving data within the database I need to verify if the person’s electronic mail has already been registrated.

perform user_id_exists($person){
    international $wpdb;

    $depend = $wpdb->get_var($wpdb->put together("SELECT COUNT(*) FROM $wpdb->users WHERE ID = %d", $person));

    if($depend == 1){ return true; }else{ return false; }
}

It must be one thing like this