You can use old stamps by selling them for cash, or using them to mail letters and packages. All you need to do is make the current postage rate.
When Do Old Stamps Expire? Royal Mail Stamp Swap Explained
Beginners Guide to Stamp Collecting - The Postal Museum
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New barcoded stamps: what you need to know
Stamps.com challenges USPS decision to end customized postage
What can I do with old first and second class stamps and when do
Can I swap my old-style stamps despite only new barcode ones being valid from 31 July?
The Cost of a Stamp Just Went Up Again - The New York Times
When did Elvis 29 stamps circulate? Are they valuable? - Quora
Can You Use Old Stamps?
Use 1st and 2nd class stamps before they expire - Skint Dad
Price of Forever Stamp on the Rise Again
Stamp shake-up spells end to buying in bulk to beat price rises - Chronicle Live
Which? - π¨ Use or swap your regular postage stamps by 31