diff --git a/cloudflare/src/better_auth.ts b/cloudflare/src/better_auth.ts
index 4552f33..1a75f10 100644
--- a/cloudflare/src/better_auth.ts
+++ b/cloudflare/src/better_auth.ts
@@ -7,24 +7,52 @@ import { jsonResponse } from "./responses.js";
 const APP_NAME = "ELY Browser";
 const AUTH_BASE_PATH = "/api/auth";
 const AUTH_CALLBACK_URL = "ely://auth/callback";
-const OTP_REQUEST_TIMEOUT_MS = 10_000;
+const EMAIL_OTP_FROM_ADDRESS = "auth@elydora.com";
+const EMAIL_OTP_EXPIRES_IN_SECONDS = 300;
 
 type BetterAuthDatabase = NonNullable<BetterAuthOptions["database"]>;
 type BetterAuthSocialProviders = NonNullable<BetterAuthOptions["socialProviders"]>;
+type VerificationOtpType = "sign-in" | "email-verification" | "forget-password" | "change-email";
+type VerificationOtpData = {
+  email: string;
+  otp: string;
+  type: VerificationOtpType;
+};
 
 export async function handleBetterAuthRoute(request: Request, env: Env): Promise<Response> {
   try {
-    return createElyAuth(env).handler(request);
+    if (requiresEmailDelivery(request)) {
+      requiredEmailBinding(env);
+    }
+    return await createElyAuth(env).handler(request);
   } catch (error) {
     if (error instanceof BetterAuthConfigError) {
       return jsonResponse({ error: "auth_unconfigured" }, 500, {
         "Cache-Control": "no-store",
       });
     }
+    if (error instanceof BetterAuthEmailDeliveryError) {
+      return jsonResponse({ error: "auth_otp_delivery_failed" }, 502, {
+        "Cache-Control": "no-store",
+      });
+    }
     throw error;
   }
 }
 
+function requiresEmailDelivery(request: Request): boolean {
+  if (request.method !== "POST") {
+    return false;
+  }
+  const path = new URL(request.url).pathname;
+  return (
+    path === `${AUTH_BASE_PATH}/email-otp/send-verification-otp` ||
+    path === `${AUTH_BASE_PATH}/email-otp/request-password-reset` ||
+    path === `${AUTH_BASE_PATH}/forget-password/email-otp` ||
+    path === `${AUTH_BASE_PATH}/email-otp/request-email-change`
+  );
+}
+
 function createElyAuth(env: Env) {
   return betterAuth({
     appName: APP_NAME,
@@ -46,7 +74,7 @@ function createElyAuth(env: Env) {
     trustedOrigins: [requiredBinding(env.ELY_AUTH_BASE_URL, "ELY_AUTH_BASE_URL"), AUTH_CALLBACK_URL],
     plugins: [
       emailOTP({
-        expiresIn: 300,
+        expiresIn: EMAIL_OTP_EXPIRES_IN_SECONDS,
         allowedAttempts: 3,
         storeOTP: "encrypted",
         resendStrategy: "rotate",
@@ -87,34 +115,88 @@ function bindingPair(
 
 async function sendVerificationOtp(
   env: Env,
-  data: {
-    email: string;
-    otp: string;
-    type: "sign-in" | "email-verification" | "forget-password" | "change-email";
-  },
+  data: VerificationOtpData,
 ): Promise<void> {
-  const endpoint = requiredBinding(env.ELY_AUTH_EMAIL_OTP_ENDPOINT, "ELY_AUTH_EMAIL_OTP_ENDPOINT");
-  const token = requiredBinding(env.ELY_AUTH_EMAIL_OTP_TOKEN, "ELY_AUTH_EMAIL_OTP_TOKEN");
-  const controller = new AbortController();
-  const timeout = setTimeout(() => controller.abort(), OTP_REQUEST_TIMEOUT_MS);
+  const sender = requiredEmailBinding(env);
   try {
-    const response = await fetch(endpoint, {
-      method: "POST",
-      headers: {
-        Authorization: `Bearer ${token}`,
-        "Content-Type": "application/json",
-      },
-      body: JSON.stringify(data),
-      signal: controller.signal,
+    await sender.send({
+      to: data.email,
+      from: { email: EMAIL_OTP_FROM_ADDRESS, name: APP_NAME },
+      subject: verificationOtpSubject(data.type),
+      html: verificationOtpHtml(data),
+      text: verificationOtpText(data),
     });
-    if (!response.ok) {
-      throw new BetterAuthEmailDeliveryError(response.status);
-    }
-  } finally {
-    clearTimeout(timeout);
+  } catch (error) {
+    throw new BetterAuthEmailDeliveryError(error);
   }
 }
 
+function verificationOtpSubject(type: VerificationOtpType): string {
+  switch (type) {
+    case "sign-in":
+      return `Your ${APP_NAME} sign-in code`;
+    case "email-verification":
+      return `Verify your ${APP_NAME} email`;
+    case "forget-password":
+      return `Reset your ${APP_NAME} password`;
+    case "change-email":
+      return `Confirm your ${APP_NAME} email change`;
+  }
+}
+
+function verificationOtpText(data: VerificationOtpData): string {
+  return [
+    `Your ${APP_NAME} ${verificationOtpAction(data.type)} code is ${data.otp}.`,
+    "This code expires in 5 minutes.",
+    "You can ignore this email if you did not request this code.",
+  ].join("\n");
+}
+
+function verificationOtpHtml(data: VerificationOtpData): string {
+  const code = escapeHtml(data.otp);
+  const action = escapeHtml(verificationOtpAction(data.type));
+  return [
+    "<!doctype html>",
+    '<html lang="en">',
+    "<body>",
+    `<p>Your ${APP_NAME} ${action} code is:</p>`,
+    `<p><strong style="font-size:24px;">${code}</strong></p>`,
+    "<p>This code expires in 5 minutes.</p>",
+    "<p>You can ignore this email if you did not request this code.</p>",
+    "</body>",
+    "</html>",
+  ].join("");
+}
+
+function verificationOtpAction(type: VerificationOtpType): string {
+  switch (type) {
+    case "sign-in":
+      return "sign-in";
+    case "email-verification":
+      return "email verification";
+    case "forget-password":
+      return "password reset";
+    case "change-email":
+      return "email change";
+  }
+}
+
+function escapeHtml(value: string): string {
+  return value
+    .replaceAll("&", "&amp;")
+    .replaceAll("<", "&lt;")
+    .replaceAll(">", "&gt;")
+    .replaceAll('"', "&quot;")
+    .replaceAll("'", "&#39;");
+}
+
+function requiredEmailBinding(env: Env): NonNullable<Env["SEND_EMAIL"]> {
+  if (env.SEND_EMAIL !== undefined) {
+    return env.SEND_EMAIL;
+  }
+  throw new BetterAuthConfigError("SEND_EMAIL");
+}
+
 function requiredBinding(value: string | undefined, name: string): string {
   if (isPresent(value)) {
     return value.trim();
@@ -134,8 +216,8 @@ class BetterAuthConfigError extends Error {
 }
 
 class BetterAuthEmailDeliveryError extends Error {
-  constructor(readonly status: number) {
-    super(`auth otp delivery failed with status ${status}`);
+  constructor(cause: unknown) {
+    super("auth otp delivery failed", { cause });
     this.name = "BetterAuthEmailDeliveryError";
   }
 }
diff --git a/cloudflare/src/bindings.ts b/cloudflare/src/bindings.ts
index 8258cc0..4175600 100644
--- a/cloudflare/src/bindings.ts
+++ b/cloudflare/src/bindings.ts
@@ -22,10 +22,18 @@ export interface ElyR2Bucket {
 export interface ElyD1PreparedStatement {
   bind(...values: unknown[]): ElyD1PreparedStatement;
   first<T = unknown>(): Promise<T | null>;
-  all<T = unknown>(): Promise<{ results: T[] }>;
+  all<T = unknown>(): Promise<ElyD1Result<T>>;
   run(): Promise<unknown>;
 }
 
+export interface ElyD1Result<T = unknown> {
+  results: T[];
+  meta?: {
+    changes?: number;
+    last_row_id?: number | null;
+  };
+}
+
 export interface ElyD1Database {
   prepare(query: string): ElyD1PreparedStatement;
   batch<T = unknown>(statements: ElyD1PreparedStatement[]): Promise<T[]>;
@@ -46,6 +54,31 @@ export interface ElyAnalyticsDataset {
   writeDataPoint(event?: ElyAnalyticsDataPoint): void;
 }
 
+export interface ElyEmailAddress {
+  email: string;
+  name: string;
+}
+
+export interface ElyEmailMessageBuilder {
+  from: string | ElyEmailAddress;
+  to: string | string[];
+  subject: string;
+  text?: string;
+  html?: string;
+  replyTo?: string | ElyEmailAddress;
+  cc?: string | string[];
+  bcc?: string | string[];
+  headers?: Record<string, string>;
+}
+
+export interface ElyEmailSendResult {
+  messageId: string;
+}
+
+export interface ElySendEmail {
+  send(message: ElyEmailMessageBuilder): Promise<ElyEmailSendResult>;
+}
+
 export interface Env {
   ELY_DB: ElyD1Database;
   ELY_KV: ElyKvNamespace;
@@ -60,6 +93,5 @@ export interface Env {
   ELY_AUTH_GOOGLE_CLIENT_SECRET?: string;
   ELY_AUTH_GITHUB_CLIENT_ID?: string;
   ELY_AUTH_GITHUB_CLIENT_SECRET?: string;
-  ELY_AUTH_EMAIL_OTP_ENDPOINT?: string;
-  ELY_AUTH_EMAIL_OTP_TOKEN?: string;
+  SEND_EMAIL?: ElySendEmail;
 }
diff --git a/cloudflare/tests/better_auth_email_otp.test.ts b/cloudflare/tests/better_auth_email_otp.test.ts
new file mode 100644
index 0000000..b7197a7
--- /dev/null
+++ b/cloudflare/tests/better_auth_email_otp.test.ts
@@ -0,0 +1,119 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+
+import type { ElyEmailMessageBuilder, Env } from "../src/bindings.js";
+import { handleRequest } from "../src/index.js";
+
+describe("better auth email otp", () => {
+  it("sends OTP through Cloudflare Email Send", async () => {
+    const sentEmails: ElyEmailMessageBuilder[] = [];
+    const response = await handleRequest(otpRequest("USER@example.com"), testEnv(sentEmails));
+
+    assert.equal(response.status, 200);
+    assert.deepEqual(await response.json(), { success: true });
+    assert.equal(sentEmails.length, 1);
+
+    const email = sentEmails[0]!;
+    assert.equal(email.to, "user@example.com");
+    assert.deepEqual(email.from, { email: "auth@elydora.com", name: "ELY Browser" });
+    assert.equal(email.subject, "Your ELY Browser sign-in code");
+    assert.match(email.text ?? "", /Your ELY Browser sign-in code is \d{6}\./);
+    assert.match(email.html ?? "", /<strong[^>]*>\d{6}<\/strong>/);
+  });
+
+  it("fails closed when the email send binding is unavailable", async () => {
+    const response = await handleRequest(otpRequest("user@example.com"), testEnv(null));
+
+    assert.equal(response.status, 500);
+    assert.deepEqual(await response.json(), { error: "auth_unconfigured" });
+  });
+});
+
+function otpRequest(email: string): Request {
+  return new Request("https://elydora.test/api/auth/email-otp/send-verification-otp", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify({ email, type: "sign-in" }),
+  });
+}
+
+function testEnv(sentEmails: ElyEmailMessageBuilder[] | null): Env {
+  const env: Env = {
+    ELY_ENVIRONMENT: "local",
+    ELY_AUTH_BASE_URL: "https://elydora.test",
+    ELY_AUTH_SECRET: "8b7f1d2b0c9a4e3f91d6c0a45e72b8f3",
+    ELY_DB: testD1Database(),
+    ELY_KV: {
+      get() {
+        return Promise.resolve(null);
+      },
+      delete() {
+        return Promise.resolve();
+      },
+    },
+    ELY_STORAGE: {
+      get() {
+        return Promise.resolve(null);
+      },
+      put() {
+        return Promise.resolve({
+          arrayBuffer() {
+            return Promise.resolve(new ArrayBuffer(0));
+          },
+        });
+      },
+      delete() {
+        return Promise.resolve();
+      },
+    },
+    ELY_RATE_LIMITER: {
+      limit() {
+        return Promise.resolve({ success: true });
+      },
+    },
+    ELY_API_AUDIT: {
+      writeDataPoint(): void {},
+    },
+    ELY_DIAGNOSTICS: {
+      writeDataPoint(): void {},
+    },
+  };
+
+  if (sentEmails !== null) {
+    env.SEND_EMAIL = {
+      send(message: ElyEmailMessageBuilder) {
+        sentEmails.push(message);
+        return Promise.resolve({ messageId: "test-message-id" });
+      },
+    };
+  }
+
+  return env;
+}
+
+function testD1Database(): Env["ELY_DB"] {
+  return {
+    prepare() {
+      return {
+        bind() {
+          return this;
+        },
+        first() {
+          return Promise.resolve(null);
+        },
+        all() {
+          return Promise.resolve({ results: [], meta: { changes: 1, last_row_id: 1 } });
+        },
+        run() {
+          return Promise.resolve({});
+        },
+      };
+    },
+    batch() {
+      return Promise.resolve([]);
+    },
+    exec() {
+      return Promise.resolve({});
+    },
+  };
+}
diff --git a/cloudflare/tests/index.test.ts b/cloudflare/tests/index.test.ts
index ea00047..70cd1ff 100644
--- a/cloudflare/tests/index.test.ts
+++ b/cloudflare/tests/index.test.ts
@@ -439,7 +439,7 @@ function testD1PreparedStatement(): ReturnType<Env["ELY_DB"]["prepare"]> {
       return Promise.resolve(null);
     },
     all() {
-      return Promise.resolve({ results: [] });
+      return Promise.resolve({ results: [], meta: { changes: 1, last_row_id: 1 } });
     },
     run() {
       return Promise.resolve({});
diff --git a/cloudflare/wrangler.toml b/cloudflare/wrangler.toml
index 06549ca..0d4c887 100644
--- a/cloudflare/wrangler.toml
+++ b/cloudflare/wrangler.toml
@@ -17,6 +17,10 @@ bucket_name = "ely-browser-storage"
 binding = "ELY_KV"
 id = "ba8f06dd5cc34bc4bc0f8a305c570cfb"
 
+[[send_email]]
+name = "SEND_EMAIL"
+allowed_sender_addresses = ["auth@elydora.com"]
+
 [vars]
 ELY_ENVIRONMENT = "production"
 ELY_AUTH_BASE_URL = "https://ely-browser-cloud.zhangyanghaha0407.workers.dev"