I would say under normal circumstances that it is okay to use your home address if you live outside of the country. If you are overseas and writing a US inmate, the odds on them knowing anyone in your native land are almost nil.

If you live in the US and are writing to American prisoners, than absolutely you should use a PO Box. Your address and any personal information you give to that inmate can be bought/sold or traded. All it takes is a letter, phone call or visit and you are no longer secure. This is realistic advice.

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"Thats it then, they will go on double, secret, probation..."