UPDATE!: I have to admit that I was already hoping for this, because following an email confirmation of my Aasiaat Radio reception I also received a letter by mail. And indeed, Bo Mogensen, head of Kystradio in Greenland (operated by Tusass), was again so kind to send a physical letter as QSL NDB OZN-372 Prins Christians Sund Greenland. Wow!!! Click here for more details about the reception of the furtherst NDB I ever logged.
Thank you Bo for this service, it is so nice to get a QSL/picture of these remote locations!
The longest distance over which I have received a beacon so far is OZN Prins Christian Sund with 3300 km. A bit of research on the internet made me think that this beacon might very well be operated by Tusass Greenland. Apparently that was correct: Bo Mogensen, who also confirmed my Aasiaat Radio reception, sent me a brief email as QSL OZN-372 Prins Christian Sund.
The OZN radio beacon is located at weather station at the Prins Christian Sund on the southern tip of Greenland. This station was founded by the US during WWII under the name Bluie East One.