It was recently reported that libidn2 can cause issues for domains whose names contain underscores, and maybe some other characters, too. It matters to us because we build GnuTLS with libidn2. I'm not sure yet what the solution is for us. Help wanted! Original report: https://github.com/systemd/systemd/issues/6426 libidn2 discussion: https://gitlab.com/libidn/libidn2/issues/30 Upstream fix: https://gitlab.com/libidn/libidn2/commit/a5cbc16efd02adb78d2d082b21c3ac4d3fa88d2e