As to the confusion about what will bew happening with DC
Delivery Confirmation service will be restricted to parcels only and will no longer be available for flat?size mail.
Means that there won't be any more delivery confirmation for the priority mail envelopes.
Delivery Confirmation options will be extended to First?Class Mail parcels.
Means that you can use it for 1st class Parcels.
To be a parcel it has to be big enough to fit on the labels and addresses on the front, and a box or be at least 3/4" thick.
Also:
. Can I drop my online label package in a USPS collection box?
A. Yes, if you have paid for postage online and printed a label with PC Postage service. If you use a postage meter, you can drop your Priority Mail item in a collection box as long as it doesn't weigh more than 5 pounds. If you are using postage stamps, aviation security requires that you take packages 16 oz. and over to your local Post Office for mailing.
from
https://sss-web.usps.com/ds/jsps/showFaq.jsp
My read on that means that if you pay for shipping online you can put it in a collection box regardless of weight. The 1lb limit is only for stamped mail.
That said, what are the thoughts about using this to send packages, since you have a much more limited reciept of mailing? Supposedly you can bring your "stub" from the label and have the post office put a postmark on it. That would be a good reciept, but wouldn't save any time, because you would still have to wait in line.
Orie