The letter was written aboard the ISS by Russian cosmonaut Roman Romanenko.
Aboard the station the letter was cancelled with the Russian round board post mark dated July 28, 2009, the day when the Shuttle Endeavour undocked from the ISS.
It was delivered to Earth by the Space Shuttle Endeavour (STS-127 flight).
Endeavour undocked from the ISS on July 28, 2009.
On July 31 Endeavour returned to Earth.
Having been delivered to Earth, the letter was posted from Houston to Russiaby registered mail.
The detailed description of the Russian round board post mark see at
www.astrophil.ucoz.ru/news/official_post_mark_cancellation_aboard_the_iss/2009-09-05-38