MI5 had a nickname of "Box" or "Box500" because postal mail was sent to "PO Box 500".
The letter would be put in an envelope. That envelope would be addressed with a department (but not a name). That envelope would then be put in another envelope. The outside envelope would be sent to Box 500.
It is kind of weird that in the 21st century we're re-learning ancient tradecraft from retired spies.
The letter would be put in an envelope. That envelope would be addressed with a department (but not a name). That envelope would then be put in another envelope. The outside envelope would be sent to Box 500.
It is kind of weird that in the 21st century we're re-learning ancient tradecraft from retired spies.