Postal Authorities use this little known surveillance technique known as the mail cover to investigate your mail without first having to obtain a court order.
The mail cover is simply an instruction to the mail carrier requesting that they note the return addresses on mail delivered to any address under investigation. With this method they easily can build a profile of the investigated person.
When using a mail drop the authority cannot see the individual letters but only the covering envelope. Building a profile is unimpossible.
We are not sure which governernments use this technique. However, the US Food & Drug Administration is definitely using it. In their Investigations Operational Manual they write:
OCI is also the point of contact for any request for a mail cover through the U.S. Postal Inspection Service. A mail cover provides a written record of all data appearing on the outside of any class of mail to obtain information for:
