First the letter was posted from the town of Khimki to Moscow. Then the letter was delivered to the ISS by the Russian "Soyuz MS-06” spacecraft. To document the delivery, on board the station the letter was marked with all proper board seals including the Russian official “Russian Post. ISS. Russian Segment” round board post mark dated September 13, 2017, the day when the “Soyuz MS-06” spacecraft docked with the ISS.