If you listen to DR Kalundborg LW 243 kHz (on air 4 times a day with
navigational warnings, weather forecasts and news) and want to send a
reception report, you can use either e-mail or ordinary mail.

Jens Christian Seeberg, in charge of sending out QSLs for Danmarks 
Radio’s LW section, has informed me, that reception reports can be sent 
to him, and he will be happy to answer them with a QSL.
E-mail: jseeberg@post3.tele.dk or
Ordinary mail: Seeberg Consult, Solbakken 9, DK-4400 Kalundborg, Denmark.
Ydun Ritz (2021-10-23)
Ydun's Medium Wave Info
https://mediumwave.info/news/
(via Mike Terry via WOR io group)