As forwarding of spam leads to numerous problems, is it possible in Plesk to prevent users from using mail forwarding options only?
Currently, there is no way to disable/hide "Mail Forwarding" option in Plesk.
Such feature already has been requested on Plesk User Voice:
Please vote this feature to increase priority of this request and future implementation. The top-ranked suggestions are likely to be included in the next versions of Plesk.