diff --git a/extensions/imessage/src/accounts.test.ts b/extensions/imessage/src/accounts.test.ts
new file mode 100644
index 00000000000..cbf60b553d6
--- /dev/null
+++ b/extensions/imessage/src/accounts.test.ts
@@ -0,0 +1,29 @@
+import { describe, expect, it } from "vitest";
+import { resolveIMessageAccount } from "./accounts.js";
+
+describe("resolveIMessageAccount", () => {
+  it("uses configured defaultAccount when accountId is omitted", () => {
+    const resolved = resolveIMessageAccount({
+      cfg: {
+        channels: {
+          imessage: {
+            defaultAccount: "work",
+            accounts: {
+              work: {
+                name: "Work",
+                cliPath: "/usr/local/bin/imsg-work",
+                dmPolicy: "open",
+              },
+            },
+          },
+        },
+      } as never,
+    });
+
+    expect(resolved.accountId).toBe("work");
+    expect(resolved.name).toBe("Work");
+    expect(resolved.config.cliPath).toBe("/usr/local/bin/imsg-work");
+    expect(resolved.config.dmPolicy).toBe("open");
+    expect(resolved.configured).toBe(true);
+  });
+});
diff --git a/extensions/imessage/src/accounts.ts b/extensions/imessage/src/accounts.ts
index 18931713eaf..5607e44bf7d 100644
--- a/extensions/imessage/src/accounts.ts
+++ b/extensions/imessage/src/accounts.ts
@@ -32,7 +32,9 @@ export function resolveIMessageAccount(params: {
   cfg: OpenClawConfig;
   accountId?: string | null;
 }): ResolvedIMessageAccount {
-  const accountId = normalizeAccountId(params.accountId);
+  const accountId = normalizeAccountId(
+    params.accountId ?? resolveDefaultIMessageAccountId(params.cfg),
+  );
   const baseEnabled = params.cfg.channels?.imessage?.enabled !== false;
   const merged = mergeIMessageAccountConfig(params.cfg, accountId);
   const accountEnabled = merged.enabled !== false;