I looked on usps web site and couldn’t find any rule stating the maximum number of stamps that may be used to post a single letter. After the recent price increase I had to get 2c stamps from a macine, which only sold them 40 at a time (20 more than I needed). So the question in the subject of this OP naturally occured to me.
I don’t know the rule, but to my mind, yes, you can certainly use as many stamps as it takes to achieve sufficient postage.
AFAIK the regulations just say “required postage.” As long as the address and return address are visible/legible.
When I was an obnoxious teenager I took one cent stamps and plastered them all over the front and back of the envelope. It was delivered. It is my belief that there is no rules about where stamps must be, they just must be visible. One little known fact is that any stamp, of any denomination, when put on a letter has a 99.9% chance of being put through provided the mailed piece did not require additional postage.
Huh? Am I the only who doesn’t quite know what you are saying in this sentence?
Yes.
They don’t have any expiration dates or anything.
In fact, I remember there was supposedly some sort of stamp collectible crash. Some companies were buying these collectible stamps at way below face value, and plastering their mail with them
What I mean is that if you take any old stamp and put in on a #10 envelope it will most likely get delivered without any notice of insufficient postage. This includes old stamps that have a face value of say 5 cents, let alone any of the many annoying stamps with no denomination on them.
There is a chance of this, but I doubt if it comes anywhere near 99%. Or even .99%. The detection equipment that the USPS uses is amazingly efficient.
Note this qualification by Silenus.
The Post Office has become more strict about the front of envelopes, partly because they do more machine reading of them.
For example, they require a clear space at the lower-left corner of the envelope, about the bottom 1/4" up from the edge, going at least halfway across the envelope. And there is supposed to be at least 1/2" clear space all the way around the delivery address. And clear space around the return address. Somewhere in my office a have a plastic template for use in checking mail designs. It’s covered with all kinds of measurements & required separations.
So I think it would be real hard to actually fit 20 stamps onto an envelope without covering parts that are technically required to be left clear. But if it’s a single envelope, the USPO would probably deliver it anyway. The postal workers really prefer to deliver mail when at all possible.
Note that at most post offices, you can exchange stamps. So if you take in a full sheet (20) 2¢ stamps, they’ll give you a 39¢ plus a penny change. Some will even exchange a partial sheet + some coins for a regular stamp. I know that I’ve exchanged a full coil of 37¢ stamps +$2 for a full coil of 39¢. One Post Office refused that, another was glad to do it.
I never tried it, but long ago, I heard that some folks (kids?) would put an envelope in the mail with a bogus “TO” address and the intended recipent’s N&A in the upper left corner. The letter would be “Returned to Sender for insufficent posstage” but the sender would be recipient.
Probably an Urban Legend. Postal employees are nlikely to be that stupid.
Damn!
The senders would put no postage on the envelope (of course).
This generally works if both addresses have the same zip code.
Postal regs require stamps to be in the upper left corner.
I thouight the return address is in the upper left and stamps are on the upper right
That’s interesting. Here the stamps go on the upper right corner.
I’m digging way back in my memory here, but as I recall the first U.S. Post Office to install automated mail sorting equipment was in Providence, R.I. They had a lot of trouble and it was constantly in the news. One of the issues was that people were using bogus stamps, one I recall was the old “Green Stamps” trading coupons. The machine could not distinguish between these and legitimate U.S. postage.
That’s probably where some of these stories got started.
I’d love to know if anyone here could give me British equivalent explanations…“No, it’s ben chewed up by the dryer, and it now looks OK, but it still has some of the ink from the serial number…”
I bought my last paintball marker from someone I met on a message board. The package cost about $7 to mail and arrived with 25% of the front slathered in little stamps. Hope that didn’t make a USPS employee count them up and hand-cancel them all.
So, yeah, it works.
With your username, you must be an expert, but I reckon you meant upper right hand corner. (or are you talking from the point of view of the postcard itself, in which case I bow to your superior knowledge and unusual point of view 
)
This was my main concern, since with 20 stamps on a standard envelope many would be some distance from the top right hand corner of the envelope.
I recently posted a parcel, not a letter, at a special temporary post office set up in a convention centre. I asked to use stamps, and they only had 39c stamps, so it was successfully posted with 22 39c stamps (a total of $8.58 postage), which pretty well covered the whole of one side of the parcel exzcept for the address label. Yes, the parcel got through – I know, because I was posting some books to myself using media mail.
I enjoy the look of envelopes slathered with stamps, so I do this occasionally (though not to the extreme of an envelope covered with, say, 51 $0.01 stamps, I will compose international postage out of lower denomination stamps, such as 2 $0.50 stamps, a $0.25 stamp, and 2 $0.10 stamps or the like).
It seems to me that postal regulations are divided into two types: 1) necessary for the mail to be delivered, violation of which will cause the piece to be rejected (sufficient postage, safety regulations, etc) and 2) necessary to make life easier for the automatic sorting machines, violation of which will cause the piece to be dumped into a bin and hand-sorted. The post office would prefer you obey such regulations, especially since your mail will get there faster that way, but it is committed to getting your mail there regardless of whether you do so or not. Little old ladies sending letters with the address written in delicate cursive and using the old-fashioned abbreviations will be happy to know this.