POSTAGE AND COURIER BUSINESS

If it is your own courier business then you can file under 44AD. ( what I mean by own business is that you are not an agent of another principle courier company nor a franchisee , and income is in the form of brokerage or commission ).
Here the aggregate gross receipts should not exceed RS.2 crore during the FY in order to get 44AD option.

If income is in the form of Commission or brokerage then 44AD is not available to you.

44ADA doesn't apply to you at all.