Online PDF Proofs are sent to the email address on the order, which is also the email address registered on the account.
If you would like your designer to check the Online PDF proof, forward the proof approval email to them for checking. It is also a good idea to have your designer view and acknowledge any additional notes that are included with the Online PDF proof.
It is the account holders responsibility to ensure that the Online PDF proof is checked carefully and approved in a timely manner.