Box number is being omitted from address line

On more than one ocation I have included a box number with a street address and when I select Ship ShipRush omits the box number on the label.
The packages were going to a physical address but needed to include a box number since the address was at a university.
Please let me know how to correct this issue so we do not have to hand write the box number on the label.

Thank you,
Heather