The alternative way to address a formal letter when the recipient's gender is unknown is to use "To whom it may concern" instead of "Dear sir/madam."
Address a judge unknown
Address Unknown - 1997 is rated/received certificates of: USA:PG
unknown
The cast of Address Unknown - 2012 includes: Matija Mates as Walter Mirrinson
in Chicago, Illinois but the address unknown
Address Unknown - 1944 is rated/received certificates of: USA:Approved USA:Passed (National Board of Review)
Address Unknown - 1995 was released on: USA: 1995 (New York City, New York)
Unknown.
unknown
You can't. You need to send it to a specific address.
In a 1907 Victorian mantion in SF,CA (Address unknown)
That answer is really unknown.