On January 27, 2011 at 14:45 UTC the Japanese HTV-2 (Kounotori - Japanese for "white stork"), unmanned supply spacecraft was docked to the ISS.
The ISS crew marked this event by canceling several covers with the board postmark dated the day of HTV docking.
It is necessary to remark that the covers were not delivered by the HTV. The covers were delivered to the ISS and then back to earth by a Russian cosmonaut aboard a Soyuz TMA spacecraft.
More details about HTV-2 docking may be read HERE.