INS "data mined" addresses on mail. Opened mail

US government kept records of addresses of citizenry and opened mail during WWII:

Consequently, [A.S. Hudson -- administrator of the Fort Lincoln Detention Station] sought authorization to bring in a full-time German-speaking intelligence officer to eavesdrop on the detainees and to gather information on the nearby populace.

Some of the citizenry, he feared, might assist in escape attempts. Intelligence work, he argued, should also include examination of the detainees' incoming and outgoing mail in order to determine their attitudes.

On the basis of this opinion, Hudson and his staff set up index cards for each detainee, recording on them the names and addresses on all outgoing mail and the writers' names, addresses, and dates of arrival on all incoming mail. This practice would soon become standard procedure at all the INS camps.

A sampling of mail was to be opened and read. In addition, the chief patrol inspector ordered incoming packages inspected for unspecified contraband prior to delivery to the Germans.