Postal Methods Changing the given address

So we sent out thousands of letters and started getting some of them returned as undeliverable. It turns out that postal methods changed the address. In one example we sent the address:

PO BOX 543

and postal methods change this to:

PO BOX 170731
BOSTON MA 02117-0961

it deleted the country as well.

Why is this happening?


Hello Sparklit, Recipient

Hello Sparklit,
Recipient addresses of mail items delivered within the United States are verified and updated by CASS-certified software to meet official USPS standards. CASS verification includes DPV as well.

Address verification corrects spelling mistakes, changes text case to uppercase, uses USPS abbreviations, completes missing information such as secondary address and ZIP+4. Most important it decreases the overall delivery time and increases the chances of successful delivery.

The corrected address automatically replaces the address provided by the user.

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