46 years ago Radio Sofia, the international service of Bulgaria, was one of the first shortwave programs I regularly listened to in the evening. Radio Sofia, now renamed to Radio Bulgaria, terminated their shortwave service in 2012. But the powerful 270 kW transmitter from Vidin on 576 kHz with the BNR Horizont program is an easy catch though. And fortunately they still issue traditional QSL cards:

fully detailed QSL from Radio Bulgaria (BNR Horizont) on 576 kHz

I sent my report to reception.report@bnr.bg and received my QSL 3 months later.