diff --git a/services/api/src/coinpay-login.test.ts b/services/api/src/coinpay-login.test.ts
new file mode 100644
index 0000000..ee2fb91
--- /dev/null
+++ b/services/api/src/coinpay-login.test.ts
@@ -0,0 +1,81 @@
+import { describe, expect, it } from 'vitest';
+import { coinpayEmail, releasableEmailHolder, resolveCoinpayUser, type CoinpayUser } from './coinpay-login.js';
+
+function fakeDb(seed: CoinpayUser[]) {
+  const rows = [...seed];
+  let n = 0;
+  return {
+    rows,
+    deps: {
+      userByCoinpaySub: async (sub: string) => rows.find((r) => r.coinpay_sub === sub) ?? null,
+      userByEmail: async (email: string) => rows.find((r) => r.email === email) ?? null,
+      createUser: async (u: { id: string; authMethod: string; coinpaySub: string; email: string | null; emailVerified: boolean }) => {
+        if (u.email && rows.some((r) => r.email === u.email)) throw new Error('duplicate key value violates unique constraint "users_email_key"');
+        rows.push({ id: u.id, auth_method: u.authMethod, coinpay_sub: u.coinpaySub, email: u.email, email_verified: u.emailVerified ? 1 : 0 });
+      },
+      newId: () => `new-${++n}`,
+    },
+  };
+}
+
+const victim: CoinpayUser = {
+  id: 'victim', auth_method: 'password', coinpay_sub: null, email: 'victim@example.com', email_verified: 1, password_hash: 'hash',
+};
+
+describe('resolveCoinpayUser', () => {
+  it('does not hand a CoinPay login the account of a victim with the same email', async () => {
+    const { deps, rows } = fakeDb([victim]);
+    const user = await resolveCoinpayUser(deps, 'attacker-sub', { sub: 'attacker-sub', email: 'victim@example.com', email_verified: true });
+    expect(user.id).not.toBe('victim');
+    expect(user.email).toBeNull();
+    expect(user.email_verified).toBe(0);
+    expect(rows.find((r) => r.id === 'victim')).toEqual(victim);
+  });
+
+  it('does not link to an account bound to another CoinPay sub', async () => {
+    const other: CoinpayUser = { id: 'other', auth_method: 'coinpay', coinpay_sub: 'sub-a', email: 'a@example.com', email_verified: 0 };
+    const { deps } = fakeDb([other]);
+    const user = await resolveCoinpayUser(deps, 'sub-b', { email: 'a@example.com' });
+    expect(user.id).not.toBe('other');
+    expect(user.coinpay_sub).toBe('sub-b');
+  });
+
+  it('returns the account bound to the sub', async () => {
+    const mine: CoinpayUser = { id: 'mine', auth_method: 'coinpay', coinpay_sub: 'sub-1', email: 'x@example.com', email_verified: 0 };
+    const { deps } = fakeDb([mine, victim]);
+    expect((await resolveCoinpayUser(deps, 'sub-1', { email: 'victim@example.com' })).id).toBe('mine');
+  });
+
+  it('never marks a CoinPay email verified, even when userinfo claims it or omits the flag', async () => {
+    const { deps, rows } = fakeDb([]);
+    await resolveCoinpayUser(deps, 's1', { email: 'one@example.com', email_verified: true });
+    await resolveCoinpayUser(deps, 's2', { email: 'two@example.com' });
+    expect(rows.map((r) => [r.email, r.email_verified])).toEqual([['one@example.com', 0], ['two@example.com', 0]]);
+  });
+
+  it('falls back to no email when it loses a race for the address', async () => {
+    const { deps, rows } = fakeDb([]);
+    const racing = { ...deps, userByEmail: async () => null };
+    rows.push({ ...victim });
+    const user = await resolveCoinpayUser(racing, 's3', { email: 'victim@example.com' });
+    expect(user.email).toBeNull();
+  });
+});
+
+describe('releasableEmailHolder', () => {
+  it('releases only an unverified, password-less CoinPay account', () => {
+    expect(releasableEmailHolder({ id: 'c', auth_method: 'coinpay', coinpay_sub: 's', email: 'e@x.io', email_verified: 0, password_hash: null })).toBe(true);
+    expect(releasableEmailHolder({ id: 'c', auth_method: 'coinpay', coinpay_sub: 's', email: 'e@x.io', email_verified: 1, password_hash: null })).toBe(false);
+    expect(releasableEmailHolder(victim)).toBe(false);
+    expect(releasableEmailHolder({ ...victim, email_verified: 0 })).toBe(false);
+    expect(releasableEmailHolder(null)).toBe(false);
+  });
+});
+
+describe('coinpayEmail', () => {
+  it('trims and rejects junk', () => {
+    expect(coinpayEmail({ email: '  a@b.co ' })).toBe('a@b.co');
+    expect(coinpayEmail({ email: 'nope' })).toBeNull();
+    expect(coinpayEmail({})).toBeNull();
+  });
+});
diff --git a/services/api/src/coinpay-login.ts b/services/api/src/coinpay-login.ts
new file mode 100644
index 0000000..b361f05
--- /dev/null
+++ b/services/api/src/coinpay-login.ts
@@ -0,0 +1,70 @@
+/**
+ * Which TronBrowser account a "Sign in with CoinPay" callback lands in.
+ *
+ * CoinPay does not verify email addresses: anyone can open a CoinPay account
+ * under someone else's address, and userinfo reports email_verified=false (or
+ * omits it). So the only identity CoinPay proves is its `sub`.
+ *
+ *  - The account bound to this sub is the one we sign into. Nothing else is.
+ *  - A new CoinPay account never takes an email another account already holds,
+ *    and its email is never marked verified, whatever CoinPay says.
+ *  - Because that email is unproven, a password signup for the same address
+ *    may take it back from a CoinPay-only account that never verified it
+ *    (see `releasableEmailHolder`), so a squatter cannot block the real owner.
+ */
+
+export interface CoinpayUser {
+  id: string;
+  auth_method: string;
+  coinpay_sub: string | null;
+  email: string | null;
+  email_verified: number;
+  password_hash?: string | null;
+}
+
+export interface CoinpayLoginDeps {
+  userByCoinpaySub(sub: string): Promise<CoinpayUser | null>;
+  userByEmail(email: string): Promise<CoinpayUser | null>;
+  createUser(u: { id: string; authMethod: string; coinpaySub: string; email: string | null; emailVerified: boolean }): Promise<void>;
+  newId(): string;
+}
+
+/** The CoinPay userinfo email, trimmed, or null. Never treated as verified. */
+export function coinpayEmail(info: Record<string, unknown>): string | null {
+  const e = typeof info.email === 'string' ? info.email.trim() : '';
+  return e && e.length <= 254 && e.includes('@') ? e : null;
+}
+
+export async function resolveCoinpayUser(
+  deps: CoinpayLoginDeps,
+  sub: string,
+  info: Record<string, unknown>,
+): Promise<CoinpayUser> {
+  const bound = await deps.userByCoinpaySub(sub);
+  if (bound) return bound;
+
+  // Never link to, and never collide with, an account that already has this
+  // address: keep the CoinPay account separate and email-less instead.
+  let email = coinpayEmail(info);
+  if (email && (await deps.userByEmail(email))) email = null;
+
+  const id = deps.newId();
+  try {
+    await deps.createUser({ id, authMethod: 'coinpay', coinpaySub: sub, email, emailVerified: false });
+  } catch (err) {
+    // Lost a race for the unique email: create the account without it.
+    if (!email) throw err;
+    email = null;
+    await deps.createUser({ id, authMethod: 'coinpay', coinpaySub: sub, email: null, emailVerified: false });
+  }
+  return { id, auth_method: 'coinpay', coinpay_sub: sub, email, email_verified: 0 };
+}
+
+/**
+ * True when `holder` keeps `email` only on CoinPay's say-so: a CoinPay-only
+ * account (no password) whose email was never verified by us. A password
+ * signup for that address may release it from the holder.
+ */
+export function releasableEmailHolder(holder: CoinpayUser | null): boolean {
+  return !!holder && holder.auth_method === 'coinpay' && !holder.password_hash && !holder.email_verified;
+}
diff --git a/services/api/src/db.ts b/services/api/src/db.ts
index cbda2cd..b0c2b45 100644
--- a/services/api/src/db.ts
+++ b/services/api/src/db.ts
@@ -84,6 +84,11 @@ export async function createUser(u: {
   });
 }
 
+/** Drop an unverified email from an account (see releasableEmailHolder). */
+export async function releaseEmail(userId: string): Promise<void> {
+  await db().execute({ sql: "UPDATE users SET email = NULL, updated_at = datetime('now') WHERE id = ? AND email_verified = 0", args: [userId] });
+}
+
 export async function setEmailVerified(userId: string): Promise<void> {
   await db().execute({ sql: 'UPDATE users SET email_verified = 1, updated_at = datetime(\'now\') WHERE id = ?', args: [userId] });
 }
diff --git a/services/api/src/index.ts b/services/api/src/index.ts
index 7eaf707..fd9c7a8 100644
--- a/services/api/src/index.ts
+++ b/services/api/src/index.ts
@@ -5,7 +5,7 @@ import { cors } from 'hono/cors';
 import { getCookie, setCookie, deleteCookie } from 'hono/cookie';
 import {
   createUser, userByCoinpaySub, userByEmail, createSession, userBySession,
-  deleteSession, putEmailToken, consumeEmailToken, setEmailVerified,
+  deleteSession, putEmailToken, consumeEmailToken, setEmailVerified, releaseEmail,
   getSettings, putSettings, type User,
 } from './db.js';
 import { token, uuid, hashPassword, verifyPassword, SESSION_TTL, EMAIL_TOKEN_TTL } from './auth.js';
@@ -16,6 +16,7 @@ import { dnsRoutes } from './dns.js';
 import { tronRelay } from './mcp/tron.js';
 import { safeRedirect } from './redirect.js';
 import { extLoginTarget } from './ext-login.js';
+import { resolveCoinpayUser, releasableEmailHolder } from './coinpay-login.js';
 import { assertDatabaseUrl, db } from './db.js';
 import { pushService } from './push/routes.js';
 import { createCrawlGate, crawlCheck } from './crawl-gate.js';
@@ -157,13 +158,9 @@ app.get('/api/auth/coinpay/callback', async (c) => {
   const sub = info.sub || info.id || tok.sub;
   if (!sub) return c.text('coinpay userinfo missing subject', 502);
 
-  const emailVerified = info.email_verified ?? !!info.email;
-  let user = await userByCoinpaySub(String(sub));
-  if (!user) {
-    const id = uuid();
-    await createUser({ id, authMethod: 'coinpay', coinpaySub: String(sub), email: info.email ?? null, emailVerified });
-    user = { id, auth_method: 'coinpay', coinpay_sub: String(sub), email: info.email ?? null, email_verified: emailVerified ? 1 : 0 };
-  }
+  // Bound to the CoinPay sub only. CoinPay never verifies emails, so its email
+  // never links to an existing account and is never marked verified.
+  const user = await resolveCoinpayUser({ userByCoinpaySub, userByEmail, createUser, newId: uuid }, String(sub), info);
   deleteCookie(c, 'cp_state'); deleteCookie(c, 'cp_redirect');
   const r = await startSession(c, user.id, redirect);
   return redirect ? r : c.redirect(`${APP_URL}/?signedin=1`);
@@ -177,7 +174,11 @@ app.post('/api/auth/signup', async (c) => {
   // The shared profile fields (first + last name required), checked before any account exists.
   const invalid = signupProfileErrors(body);
   if (invalid) return c.json(invalid, 400);
-  if (await userByEmail(email)) return c.json({ error: 'email already registered' }, 409);
+  const holder = await userByEmail(email);
+  if (holder && !releasableEmailHolder(holder)) return c.json({ error: 'email already registered' }, 409);
+  // A CoinPay-only account holding this address on CoinPay's unverified word
+  // gives it up; the new account still has to verify it by email.
+  if (holder) await releaseEmail(holder.id);
   const id = uuid();
   await createUser({ id, authMethod: 'password', email, passwordHash: hashPassword(password), emailVerified: false });
   await saveSignup(profileStore(), id, body, email);