Yesterday, I received an IRS audit report that was mailed, first class, on June 6 from zip code 94903 to 95747, both in CA.
It had a Japanese meter stamp from Hayama, Japan, 670 yen, dated June 29. Handwritten below the address window was "USA".
It also had a blue "Air Mail" stamped on the envelope. I assume that was applied here.
This is the second time something like this has happened. Last year, it was a client's large envelope that went the same route.
There may be a problem with the bar code strip, or the code reader. Those strips are applied by the sender (IRS).