diff --git a/apps/web/utils/outlook/client.emulator.test.ts b/apps/web/utils/outlook/client.emulator.test.ts
new file mode 100644
index 0000000000..a1d75322c0
--- /dev/null
+++ b/apps/web/utils/outlook/client.emulator.test.ts
@@ -0,0 +1,65 @@
+import { createServer, type Server } from "node:http";
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+describe("OutlookClient with Microsoft emulator", () => {
+  let server: Server | undefined;
+
+  afterEach(async () => {
+    vi.doUnmock("@/env");
+    vi.doUnmock("@/utils/auth/save-tokens");
+    vi.doUnmock("@/utils/auth/cleanup-invalid-tokens");
+    vi.resetModules();
+
+    if (server) {
+      await new Promise<void>((resolve, reject) => {
+        server?.close((error) => {
+          if (error) reject(error);
+          else resolve();
+        });
+      });
+    }
+  });
+
+  it("authorizes requests to an HTTP Microsoft emulator", async () => {
+    let authorizationHeader: string | undefined;
+
+    server = createServer((request, response) => {
+      authorizationHeader = request.headers.authorization;
+      response.writeHead(200, { "content-type": "application/json" });
+      response.end(JSON.stringify({ id: "user-id" }));
+    });
+
+    const port = await new Promise<number>((resolve, reject) => {
+      server?.listen(0, "127.0.0.1", () => {
+        const address = server?.address();
+        if (typeof address === "object" && address) resolve(address.port);
+        else reject(new Error("Failed to start test server"));
+      });
+    });
+
+    vi.doMock("@/env", () => ({
+      env: {
+        MICROSOFT_BASE_URL: `http://127.0.0.1:${port}`,
+        NODE_ENV: "test",
+      },
+    }));
+    vi.doMock("@/utils/auth/save-tokens", () => ({
+      saveTokens: vi.fn(),
+    }));
+    vi.doMock("@/utils/auth/cleanup-invalid-tokens", () => ({
+      cleanupInvalidTokens: vi.fn(),
+    }));
+
+    const [{ createOutlookClient }, { createScopedLogger }] = await Promise.all(
+      [import("./client"), import("@/utils/logger")],
+    );
+
+    const client = createOutlookClient(
+      "emulator-token",
+      createScopedLogger("test"),
+    );
+    await client.getClient().api("/me").get();
+
+    expect(authorizationHeader).toBe("Bearer emulator-token");
+  });
+});
diff --git a/apps/web/utils/outlook/client.test.ts b/apps/web/utils/outlook/client.test.ts
index 70a4151fa9..807654d03f 100644
--- a/apps/web/utils/outlook/client.test.ts
+++ b/apps/web/utils/outlook/client.test.ts
@@ -1,5 +1,5 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
-import { Client } from "@microsoft/microsoft-graph-client";
+import { Client, MiddlewareFactory } from "@microsoft/microsoft-graph-client";
 import { saveTokens } from "@/utils/auth/save-tokens";
 import { createTestLogger } from "@/__tests__/helpers";
 import {
@@ -16,6 +16,10 @@ import {
 vi.mock("@microsoft/microsoft-graph-client", () => ({
   Client: {
     init: vi.fn(),
+    initWithMiddleware: vi.fn(),
+  },
+  MiddlewareFactory: {
+    getDefaultMiddlewareChain: vi.fn(() => [{}]),
   },
 }));
 
@@ -66,8 +70,10 @@ describe("outlook client emulator configuration", () => {
     expect(getMicrosoftGraphClientOptions).toHaveBeenCalledWith(
       "emulator-token",
     );
-    expect(Client.init).toHaveBeenCalledWith({
-      authProvider: expect.any(Function),
+    expect(MiddlewareFactory.getDefaultMiddlewareChain).toHaveBeenCalledWith({
+      getAccessToken: expect.any(Function),
+    });
+    expect(Client.initWithMiddleware).toHaveBeenCalledWith({
       baseUrl: "http://localhost:4003/",
       customHosts: new Set(["localhost"]),
       defaultVersion: "v1.0",
@@ -77,6 +83,7 @@ describe("outlook client emulator configuration", () => {
           Prefer: 'IdType="ImmutableId"',
         },
       },
+      middleware: [expect.any(Object)],
     });
   });
 
diff --git a/apps/web/utils/outlook/client.ts b/apps/web/utils/outlook/client.ts
index ba7c6bcfea..cdc108e738 100644
--- a/apps/web/utils/outlook/client.ts
+++ b/apps/web/utils/outlook/client.ts
@@ -1,4 +1,9 @@
-import { Client } from "@microsoft/microsoft-graph-client";
+import {
+  Client,
+  MiddlewareFactory,
+  type Context,
+  type Middleware,
+} from "@microsoft/microsoft-graph-client";
 import type { User } from "@microsoft/microsoft-graph-types";
 import { saveTokens } from "@/utils/auth/save-tokens";
 import { cleanupInvalidTokens } from "@/utils/auth/cleanup-invalid-tokens";
@@ -27,11 +32,7 @@ export class OutlookClient {
     this.accessToken = accessToken;
     this.logger = logger;
     const graphClientOptions = getMicrosoftGraphClientOptions(accessToken);
-    this.client = Client.init({
-      authProvider: (done) => {
-        done(null, this.accessToken);
-      },
-      defaultVersion: "v1.0",
+    const clientOptions = {
       ...graphClientOptions,
       // Use immutable IDs to ensure message IDs remain stable
       // https://learn.microsoft.com/en-us/graph/outlook-immutable-id
@@ -41,6 +42,22 @@ export class OutlookClient {
           Prefer: 'IdType="ImmutableId"',
         },
       },
+    };
+
+    if (graphClientOptions.baseUrl) {
+      this.client = Client.initWithMiddleware({
+        ...clientOptions,
+        middleware: getMicrosoftEmulatorMiddleware(accessToken),
+      });
+      return;
+    }
+
+    this.client = Client.init({
+      authProvider: (done) => {
+        done(null, this.accessToken);
+      },
+      defaultVersion: "v1.0",
+      ...clientOptions,
     });
   }
 
@@ -258,3 +275,41 @@ export function getLinkingOAuth2Url() {
 
 // Helper types for common Microsoft Graph operations
 export type { Client as GraphClient };
+
+function getMicrosoftEmulatorMiddleware(accessToken: string) {
+  const middleware = MiddlewareFactory.getDefaultMiddlewareChain({
+    getAccessToken: async () => accessToken,
+  });
+
+  // Graph SDK 3.x only authenticates HTTPS custom hosts, while emulate.dev
+  // intentionally serves its local Microsoft endpoint over HTTP.
+  middleware[0] = new MicrosoftEmulatorAuthenticationHandler(accessToken);
+
+  return middleware;
+}
+
+class MicrosoftEmulatorAuthenticationHandler implements Middleware {
+  private readonly accessToken: string;
+  private nextMiddleware: Middleware | undefined;
+
+  constructor(accessToken: string) {
+    this.accessToken = accessToken;
+  }
+
+  setNext(nextMiddleware: Middleware) {
+    this.nextMiddleware = nextMiddleware;
+  }
+
+  async execute(context: Context) {
+    context.options ??= {};
+    const headers = new Headers(context.options.headers);
+    headers.set("Authorization", `Bearer ${this.accessToken}`);
+    context.options.headers = headers;
+
+    if (!this.nextMiddleware) {
+      throw new Error("Microsoft emulator middleware chain is incomplete");
+    }
+
+    await this.nextMiddleware.execute(context);
+  }
+}