To enable delivery receipts by default, or to add a signature by default to new packages:
In the top banner, click MY ACCOUNT, Locate the Edit Your Ad Hoc Transfer Settings... section.
Options:
Enable Delivery Receipts by default. All new, replied, or forwarded packages show a Delivery Receipt. Note: When you send a new package, you can disable delivery receipts for that package.
Ad Hoc Transfer Signature: Enter a signature to append to all new packages that you create.