Return detailed ACS error responses

src/worker.ts

@@ -134,12 +134,24 @@ const handleContact = async (request: Request, env: Env) => {
         },
     );
     if (!response.ok) {
-        const errorText = await response.text();
+        const contentType = response.headers.get("content-type") ?? "";
+        const errorText = contentType.includes("application/json")
+            ? JSON.stringify(await response.json().catch(() => ({})))
+            : await response.text();
+        const errorCode = response.headers.get("x-ms-error-code");
+        const details = [
+            `${response.status} ${response.statusText}`.trim(),
+            errorCode ? `code=${errorCode}` : "",
+            errorText.trim(),
+        ]
+            .filter(Boolean)
+            .join(" | ")
+            .slice(0, 500);
         return jsonResponse(
             {
                 ok: false,
                 error: "Failed to send email.",
-                details: errorText.slice(0, 500),
+                details,
             },
             502,
         );