The feature is
either to forward
or to delete upon detection of a keyword(s)
but not combined.

That is, what we want is that incoming email is to be forwarded AND deleted

This feature is already in cPanel emails
but surprisingly so called premium business email this feature is lacking.

Quite many features that are already in cPanel are not in PBE.
Is it possible that you may also list down the reasons
that your customers are opting for PBE
instead of cPanel email system,
BESIDE the reason of separate disk space for PBE
???