youdao

The address is unknown to me.

地址未详。

《新英汉大辞典》

These rogue Internet pharmacies are operated internationally, they have no registered business address and sell products that have an unknown or unclear origin.

这些流氓因特网药店是国际性经营，它们没有任何注册营业地址，出售的产品产地不明或不清。

youdao

If you ask me, I think Elvis said it best about such messages: Return to sender, address unknown, no such number, no such zone.

FORBES: Elvis Presley Had It Right When It Came To Insider Trading

The changes affect not only Delaware residents, but also any shareholder of a Delaware-incorporated company whose current address is unknown to the issuer or is a foreign address, including U.S. military personnel stationed abroad.

WSJ: State Governments Eye 'Inactive' Broker Accounts