if I have a contact form sending an email from my WordPress site, I MUST send it to the email address created through cpanel that is directly associated with the Bluehost domain. Right?
Of course not. Send it to any email address you choose.
At this point, I can successfully send test emails from within the WP-Mail-SMTP plugin
That's odd, because your SMTP host is wrong:
SMTP Host: box###.bluehost.comI'm pretty sure that should be mail.thedomain.com.
And the contact form doesn't send ANY emails. It fails every time.
WP Mail SMTP won't show you what the error is from Contact Form 7, but this plugin will : https://wordpress.org/plugins/postman-smtp/