This was my fourth attempt in the last 12 months and finally successful: QSL Hai Phong Radio 8414.5 kHz. They were broadcasting a DSC message to cargo ship “Ga Hong” on the South Chinese Sea. I sent my report to firstname.lastname@example.org . It is only my 2nd QSL from Vietnam. The other one is from the Voice of Vietnam, years ago.
Hai Phong Radio is probably the station from Vietnam that I receive most often. Ho Chi Minh Radio is another regular one. I received Nha Trang Radio once on 8 MHz. This station apparently doesn’t operate on higher frequencies. I sent reports to these latter two stations via regular mail, but never received a reply. So if someone has a good (email)address, feel free to put it in the comments.