Blacklist all incoming email except for a few whitelisted addresses

I have a client that gets massive amounts of spam daily. Spamassassin is blocking over 700 a day but many are getting through still. I have his setting at 2. It was catching 80-90% until around September, then the spammers apparently started using new techniques to get past spamassassin with low scores.

He has started a new g*ail account, (let them filter it instead of me ), but I need to keep his current email account active as it has thousands of critical emails sorted in IMAP folders. I do not want any new spam emails to this account and I want to blacklist all incoming mail except for a few addresses. (like me)

Can I use "account level filtering" in CPanel, ie "From" "contains" "*.*" "Discard Message", with the allowed addresses in rules above it, or should I use spamassassin to blacklist *@* and then allow 3 whitelisted addresses?

I thought about creating an EXIM filter but I don't know how to isolate those rules to just one account. My cpanel_exim_system_filter_custom is at 98kb with rules and it works great across all my domains. I just can't keep up with all the new spam, just the most used ones. "Whack a mole" is never ending .

Thank You!

 

Thanks for the suggestion.
I had disabled it in Tweak Settings years ago. It is ok for a personal account but creates problems with a commercial account.

Boxtrapper may be the answer. It does look like a lot of manual labor when a simple rule might take care of it automatically.

I am compiling BoxTrapper white list entries.
He is on many automatic mailing lists that will not respond to boxtrapper's request.
I guess I'll have to log into his IMAP account and go through the emails.
He does not have the time to do this himself.
Looks like a long day...