How common is this? I know I've received at least one large envelope (not books) where the postage wasn't cancelled- so I used it again (bad, I know), mostly out of curiosity, and it was sent. Now the same thing just happened with my sister, where I'd sent her an envelope with my address on it, but the postage was pre-printed by the company I'd ordered from, and instead of blacking everything out and putting her own stamps on it, my sister (probably innocently) just put some stuff in it and mailed it back to me. Once again, it was delivered. I thought for SURE that pre-printed postage with a bar code would be "cancelled" electronically or something once delivered, but it seems like it wasn't? 

I guess I was just wondering if uncancelled postage is an area where the P.O. might not even be aware they're losing funds?

I also was not aware pre-printed postage could be re-used.  If it was a permit number, the origional shipper might have been charged again.

I receive quite a few packages with stamps that are not cancelled, I mark through them with a permanent marker (so as not to tempt DH to re-use them). 

You might want to be more careful not to reuse postage in the future, it's theft, and they can probably impose a hefty fine if you get caught.  Like defacing mailboxes, it's a federal crime (not local ordinances).

I've never seen it canceled. The information for mailing is in the indicium. It doesn't need to be canceled because the information in it tells them when you are reusing already used postage. Should the USPS scan that they will find you are reusing postage and at a minimum deliver it postage due. They could tell you you are committing postal fraud. Pre-paid labels are usually also dated, which the USPS shouldn't accept more than a couple of days after that date has passed.

I am guessing that Denise may be correct that the preprinted postage from the company may have had their permit charged again. You may get a call from the company asking why there was a package delivered to you using that label again.

Preprinted postage sometimes gets through. But I have seen members post where someone sending them a book, re-used their label by accident and it arrived postage due so it doesn't always get through.

Okay... I have a friend who gets a LOT of package mail over the course of a month. We have a deal going where I take his recyclables to the proessing center and he saves all his padded envelopes for me to reuse. (Saves me a TON of money both here and on eBay.) Many, many, many times, there are uncancelled stamps - not pre-paids or postage meter labels, but good, old-fashioned stamps. Although I have never reused them, there have been times when I have been tempted... especially when the padded envelope is clean and in really good shape.  That said, I know that all of the local USPS branches around here, (Jefferson County WV), have always hand-cancelled every piece of mail that I've sent with stamps on them. As a side-note, a local Postmaster told me that not only is it considered mail fraud to reuse a stamp, it's also against the rules to peel an unused stamp off of an envelope or package and re-affix it to something else. Also, once you buy stamps, they are yours; the USPS will not buy them back from you. At least, none of the branches around here will, anyway.

I have gotten several packages of books from PBS members  with stamps affixed as postage that weren't cancelled--it just floors me cause you know there are people who are reusing stamps/wrappers they receive like that. However, my PO clerks tell me if you put a stamp on an envelope but never mail it, you CAN peel it off to use on another envelope or package.

"However, my PO clerks tell me if you put a stamp on an envelope but never mail it, you CAN peel it off to use on another envelope or package."

Apparently, they aren't supposed to tell you that. Since posting my comment on the 7th, I mentioned the topic to a Postmaster at another branch. (With the recent e-DC debacle, I seem to be talking to a lot of different USPS employees about USPS policies instead of fun stuff, like tonight's Westminster Kennel Club Dog Show.)

Anyway, she confirmed that since the USPS has no way to know if a re-affixed stamp is new or has been used, the "party line" is to tell patrons that once a stamp is affixed, it cannot be peeled off and reused. HOWEVER, if it's not readily obvious that your (unused) stamp has been peeled off and re-affixed, I say, "Go for it!"