Can anyone explain whether the following message from the USPS means that I should put my return address both on the outside and on the inside of an envelope? I have never heard of the need to do this in the case of an envelope.
https://www.dropbox.com/s/kra6...0the%20USPS.png?dl=0

that link you posted looks to be spam
however the post office has always wanted a address inside of packages not letters. this is so if the package gets wet and the address get messed up it can be opened, and a good address found.

Thank you for the explanation. Now I understand that the recommendation to put an address label applies primarily to parcels rather than letters.
The screenshot contains a genuine message from the USPS, which was sent to me after the USPS had not been able to find my letter which I had reported as lost in transit. A compensation of about $50 was also sent to me here in Russia.