We do live at 9 West Street not Road and Cambridge, MA not England.
You'd think that with a 90c stamp, England underlined, and an unrecognized zip code....
Now I do know that the way mail is processed is as follows:
At the receiving mail center, the envelope is scanned and an orange identifying bar code is printed on the back. The address image is sent to some place where people figure out the 9 digit zip code and carrier route code and type it into a database. Later the envelope is scanned again this time looking at the orange bar code and the new bar code and 9 digit zip is printed on the front. Then the envelope goes through a sorting machine where it is directed to be sent to the mail center of the addressee.
At the mail center of the addressee, it goes through another scanner/sort process with the rest of mail received from other places and eventually comes out in carrier walking order to be sent to the destination post office. The carrier then takes this pile along with the non-first class mail which he still has to sort (but that is about to be automated in Boston) and puts it in his mail bag. He also has to check the mail to see if the address is on the hold or forwarding list (this is also soon to be automated and the forwarding will be discovered back at the originating mail center). For forwarding it goes back to get its new label printed and then gets back into the mail stream. For hold he puts it in a bin. When they automate the forwarding and hold stuff that should correct lots of the failures of that type which are completely dependent upon the carrier and often fails when there is a non-regular substitute carrier.
The carrier is supposed to to look at every piece but since much of the mail is presorted he probably doesn't do it.
The original error was by the person who looked up the address, and the carrier is the check point for catching such an error.
And no, even though I was curious about a letter from an Appeals court to the Faculty of English I didn't commit a mail crime and open it.