Forwarding INBOX email only

[demouser]

People (and spammers) send email to [email protected].
It gets forwarded to [email protected] (not my idea, but that's what they want)
EVERYTHING gets forwarded. No filtering is applied.

I want to apply my cPanel global email filters first and then forward the emails.
A workaround would be to simply forward [email protected] because that is already filtered.
The problem is cPanel does not consider email folders to be valid email addresses.

Seems like a simple request, but I can't find a cPanel or SpamAssassin setting for it and my hosting company says "I simply need to write DMARC record", which I would have to learn about.
Any thoughts?