Generally international tracking numbers should comply to unified UPU standard called S10. In accordance with this standard, each tracking number should have a check-digit (or checksum). Check-digit is necessary to avoid any mistakes in processing emails by some automatic sorting systems. So, if you like international shopping, it is good idea to check correctness of your tracking number right after you get it from a seller.
You need to remember that some small postal services (for example, WeDo Express) don't follow international standards and checksum for their tracking numbers will always be wrong.
You can check correctness of your tracking number with the help of our extension. The extension can also show information about your packages and has much more useful features.
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