Question about migration from O365 tenant to On-prem EX2016

When setting up the migration plan in ODME using source O365 and target on-prem Ex2016, I'm unable to apply any forwarding on the source O365 mailbox.  The options for forwarding (optional) are completely greyed out.  I understnad that ODME can't apply forwarding on on-prem exch servers, but since my source is O365 why wouldn't ODME let me apply forwarding on the source?