Database query very slow, missing join ON clause

Using the latest version available of this plugin. On a large database with 18k rows in posts table, and 1.4 million in postmeta, this query was taking 1800+ seconds and getting killed by pt-kill.

# Query_time: 1837.006869  Lock_time: 0.000001 Rows_sent: 0  Rows_examined: 1233843
SELECT
            DISTINCT(ID)
        FROM wp_posts

        INNER JOIN wp_postmeta as pm

        WHERE post_type="flamingo_inbound"
        AND ( TIMESTAMPDIFF(DAY, post_date, NOW()) ) >= 5
        AND ( (pm.meta_key = "_submission_status" AND pm.meta_value ="spam") OR post_status="flamingo-spam" )
        LIMIT 0, 10000;

There doesn’t appear to be an ON clause describing how the two tables are joined. It looks like it needs this added:
ON pm.post_id=wp_xbxhw9_posts.id

This would appear to take the rows examined from billions to more in the 200k rows, and from 1800+ seconds to 1.12 seconds.

Not sure this is the best code fix, but a potential fix is in file inazo-flamingo-automatically-delete-old-messages.php, line 171, add:

ON pm.post_id = '.$wpdb->prefix.'posts.ID

Let me know if you have further questions. I hope this can speed up other users of this plugin.