Receipt For Postage Due Or What?

Can anyone enlighten what this might be other than some type of receipt for postal expenses? Postage due? Extra services?

There is a light rubber stamped marking visible under the post marks with a portion of it obscured by the $1.00 Patrick Henry stamp. What is visible is "Form 35??" with the question marked portion obscured by the stamp. Below that is ".40"(¢) and "Post??" again with the question marked portion covered by the $1.00 stamp.

No markings on reverse.

Thanks in advance for any input.

There were a number of postal forms in the 35xx range dealing with address corrections, address changes, etc. In many cases the publishers were willing to pay to be notified when a client moved. In your case they apparently got back 4 forms at 40 cents each (a high fee, so a somewhat suspect interpretation), but the total postage is 1.80, so there is more here to interpret - perhaps more math covered by the lower stamp. It would be useful to know the complete form # on the envelope, which might better help identify the rate/contents. And it may have been a combination of notifications - or just an envelope used as a piece or scratch paper, which without the contents or attachments will be very challeging to tease-out.

In another simpler case, here is an envelope containing copies of Form 3579 (undeliverable 2nd, 3rd, 4th class matter; later retitled to undeliverable Standrad Mail A and B and Special Standard Mail B), which was received back by the publisher c1983 with 1 address notice and a charge of 25 cents at that time.

This cover appears to be addressed to a newspaper, so the postage might relate to sending multiple mailings of some kind. Or it might be the top cover in a stack.