Additional suggestions here that applies whether you print your postage or not. Delivery Confirmation can't be done for first class "letters" or "flats" (large envelopes), but can be used in connection with Priority Mail of any thickness, and with "parcels". So if you want Delivery Confirmation on a thin mailing, and don't want to pay the high Priority Mail fees, I suggest this -- put some cardboard or those Styrofoam peanuts in the envelope to build it up over 3/4" thick, so you can use Delivery Confirmation in connection with "parcels" (up to 13 ounces), which must be over 3/4" thick.

Likewise with the eBay-PayPal postage-shipping labels: build up the thickness of the envelope (over 3/4") so you get the benefit of the cheap Delivery Confirmation, and also insurance (at post office regular rates) if you want insurance. (PayPal-eBay's postage-label set-up doesn't allow you to send first class "letters" or first class "flats," only first class "parcels" and packages.)

Robert