Hi,
Do you mean you want to show flagged items from a second resource mailbox in the To-Do list? Do you want to show flagged items only from the second resource mailbox in the To-Do list? If this is the case, we can try applying the following filter:
1. Open the View Settings dialog for the To-Do Bar via right-clicking on the "Arrange By" column header and choose "View Settings".
2. Click Filter button.
3. Click Advanced tab.
4. Add the following criteria:
Field: E-mail Account
Condition: is (exactly)
Value: <resource mailbox Name>
5. Click "Add to List" button. Click OK.
6. Click OK.
If I've misunderstood something, please feel free to let me know.
Regards,
Steve Fan
TechNet Community Support