To enable automatic forward of all your email from your Apple iCloud mailbox:
- Log into your iCloud mailbox
- Click the Action pop-up menu in the sidebar, then choose Preferences.
- In the General pane, select Forward my email to then type the forwarding address in the text field.
- If you don’t want to store a copy of each forwarded message in iCloud, select Delete messages after forwarding.
- Click Done.
To forward only specific emails, see Filter email automatically.
Reference: iCloud: Forward all messages automatically