To set up email forwarding, select 'Mail', then choose the email account you want to forward. Click on the 'Forwarding' tab, tick the 'Switch on mail forwarding' box, and enter the email address you want to forward emails to. Click 'OK' to save the changes.
https://docs.plesk.com/en-US/obsidian/administrator-guide/website-management/mail-settings.70616/