fix: allow underscores during IDNA conversion

main.go

@@ -326,11 +326,13 @@ All long form (--) flags can be toggled with the dig-standard +[no]flag notation
 		// Skip if already an in-addr.arpa or ip6.arpa name
 		lowerName := strings.ToLower(opts.Name)
 		if !strings.HasSuffix(lowerName, ".in-addr.arpa") && !strings.HasSuffix(lowerName, ".ip6.arpa") {
-			asciiName, err := idna.Lookup.ToASCII(opts.Name)
+			// Allow underscores during IDNA conversion
+			_asciiName := strings.ReplaceAll(opts.Name, "_", "..")
+			asciiName, err := idna.Lookup.ToASCII(_asciiName)
 			if err != nil {
 				return fmt.Errorf("idna toascii: %s", err)
 			}
-			opts.Name = asciiName
+			opts.Name = strings.ReplaceAll(asciiName, "..", "_")
 		}
 	}
 

main_test.go

@@ -612,3 +612,16 @@ func TestMainTypeNotation(t *testing.T) {
 	assert.Nil(t, err)
 	assert.Regexp(t, regexp.MustCompile(`cloudflare.com. .* HTTPS .*`), outType65.String())
 }
+
+func TestIDNAUnderscoreASCII(t *testing.T) {
+	// Ensure ASCII names with underscores are not mangled by IDNA processing
+	out, err := run(
+		"--all",
+		"-q", "_acme-challenge.example.com",
+		"-t", "TXT",
+	)
+	assert.Nil(t, err)
+	// Expect the question or answer to include the literal underscore name
+	re := regexp.MustCompile(regexp.QuoteMeta("_acme-challenge.example.com."))
+	assert.Regexp(t, re, out.String())
+}