diff --git a/.env.example b/.env.example
index e3c9986..2db1faa 100644
--- a/.env.example
+++ b/.env.example
@@ -1,4 +1,4 @@
-# Google OAuth Web client (gmail.readonly)
+# Google OAuth Web client (gmail.modify)
 GOOGLE_CLIENT_ID=
 GOOGLE_CLIENT_SECRET=
 
@@ -14,8 +14,14 @@ SESSION_SECRET=change-me-to-a-long-random-string
 PORT=3000
 NODE_ENV=development
 
+# Optional default mailbox when CLI omits --user (else users.is_default / sole account)
+# GMAIL_DEFAULT_USER=you@gmail.com
+
 # Watcher (apps/watcher) — Gmail Pub/Sub push
 WATCHER_PORT=3001
+# Only these mailboxes get INBOX watch + receipt parsing (comma-separated).
+# Empty / unset = all connected accounts. CLI (npm run gmail) is unaffected.
+WATCHER_MAILBOXES=eleven16th@gmail.com
 # Full topic name, e.g. projects/my-gcp-project/topics/gmail-push
 # A short name like gmail-push is expanded if GOOGLE_CLOUD_PROJECT is set.
 GOOGLE_PUBSUB_TOPIC=
diff --git a/apps/watcher/src/config.js b/apps/watcher/src/config.js
index 6ccbf4e..d7e119a 100644
--- a/apps/watcher/src/config.js
+++ b/apps/watcher/src/config.js
@@ -20,6 +20,36 @@ export const GOOGLE_CLOUD_PROJECT =
 export const PUBSUB_VERIFICATION_TOKEN =
   process.env.PUBSUB_VERIFICATION_TOKEN || "";
 export const SQLITE_PATH = process.env.SQLITE_PATH || defaultSqlitePath;
+/** Optional default mailbox email when scripts omit --user */
+export const GMAIL_DEFAULT_USER = (process.env.GMAIL_DEFAULT_USER || "").trim();
+
+/**
+ * Parse comma-separated mailbox allowlist for the receipt watcher.
+ * Empty / unset → empty Set (caller treats as "allow all").
+ */
+export function parseWatcherMailboxes(raw) {
+  const set = new Set();
+  for (const part of String(raw || "").split(",")) {
+    const email = part.trim().toLowerCase();
+    if (email) set.add(email);
+  }
+  return set;
+}
+
+/** Lowercased emails allowed for Pub/Sub receipt watch. Empty = all connected accounts. */
+export const WATCHER_MAILBOXES = parseWatcherMailboxes(
+  process.env.WATCHER_MAILBOXES,
+);
+
+/**
+ * @param {string|null|undefined} email
+ * @param {Set<string>} [allowlist=WATCHER_MAILBOXES]
+ */
+export function isWatcherMailboxAllowed(email, allowlist = WATCHER_MAILBOXES) {
+  if (!allowlist || allowlist.size === 0) return true;
+  if (!email) return false;
+  return allowlist.has(String(email).trim().toLowerCase());
+}
 
 export const POCKETBASE_URL = (process.env.POCKETBASE_URL || "").replace(
   /\/$/,
diff --git a/apps/watcher/src/index.js b/apps/watcher/src/index.js
index 048d08f..38d8f2b 100644
--- a/apps/watcher/src/index.js
+++ b/apps/watcher/src/index.js
@@ -1,5 +1,12 @@
 import Fastify from "fastify";
-import { GOOGLE_PUBSUB_TOPIC, PORT, WATCH_RENEW_MS, assertConfig } from "./config.js";
+import {
+  GOOGLE_PUBSUB_TOPIC,
+  PORT,
+  WATCH_RENEW_MS,
+  WATCHER_MAILBOXES,
+  assertConfig,
+  isWatcherMailboxAllowed,
+} from "./config.js";
 import { listUsersWithTokens } from "./db.js";
 import { startWatch } from "./google.js";
 import { fetchAndLogMessage } from "./handlers/fetch-and-log-message.js";
@@ -44,7 +51,22 @@ async function renewAllWatches() {
     app.log.warn("gmail-watch: no signed-in users with tokens");
     return;
   }
+
+  if (WATCHER_MAILBOXES.size > 0) {
+    app.log.info(
+      { allowlist: [...WATCHER_MAILBOXES] },
+      "gmail-watch: WATCHER_MAILBOXES restrict receipt watches",
+    );
+  }
+
   for (const user of users) {
+    if (!isWatcherMailboxAllowed(user.email)) {
+      app.log.info(
+        { userId: user.id, email: user.email },
+        "gmail-watch: skip watch (not in WATCHER_MAILBOXES)",
+      );
+      continue;
+    }
     try {
       await startWatch(user.id);
       app.log.info(
diff --git a/apps/watcher/src/routes/pubsub.js b/apps/watcher/src/routes/pubsub.js
index 41c7afb..649a908 100644
--- a/apps/watcher/src/routes/pubsub.js
+++ b/apps/watcher/src/routes/pubsub.js
@@ -1,5 +1,5 @@
 import { timingSafeEqual } from "node:crypto";
-import { PUBSUB_VERIFICATION_TOKEN } from "../config.js";
+import { PUBSUB_VERIFICATION_TOKEN, isWatcherMailboxAllowed } from "../config.js";
 import { getUserByEmail, getWatchState, saveWatchState } from "../db.js";
 import {
   gmailClientForUser,
@@ -71,6 +71,14 @@ function decodeNotification(body) {
 }
 
 async function processNotification(log, { fetchHandlers, processHandlers }, notification) {
+  if (!isWatcherMailboxAllowed(notification.emailAddress)) {
+    log.warn(
+      { email: notification.emailAddress },
+      "gmail-watch: mailbox not in WATCHER_MAILBOXES, acking",
+    );
+    return;
+  }
+
   const user = getUserByEmail(notification.emailAddress);
   if (!user) {
     log.warn(
diff --git a/apps/watcher/test/watcher-mailboxes.test.js b/apps/watcher/test/watcher-mailboxes.test.js
new file mode 100644
index 0000000..2b67c56
--- /dev/null
+++ b/apps/watcher/test/watcher-mailboxes.test.js
@@ -0,0 +1,46 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import {
+  isWatcherMailboxAllowed,
+  parseWatcherMailboxes,
+} from "../src/config.js";
+
+describe("parseWatcherMailboxes", () => {
+  it("returns empty set for blank input", () => {
+    assert.equal(parseWatcherMailboxes("").size, 0);
+    assert.equal(parseWatcherMailboxes(null).size, 0);
+    assert.equal(parseWatcherMailboxes("  ,  ").size, 0);
+  });
+
+  it("normalizes and splits emails", () => {
+    const set = parseWatcherMailboxes(
+      " Eleven16th@gmail.com , other@Example.COM ",
+    );
+    assert.deepEqual([...set].sort(), [
+      "eleven16th@gmail.com",
+      "other@example.com",
+    ]);
+  });
+});
+
+describe("isWatcherMailboxAllowed", () => {
+  it("allows all when allowlist is empty", () => {
+    const empty = new Set();
+    assert.equal(isWatcherMailboxAllowed("anyone@x.com", empty), true);
+    assert.equal(isWatcherMailboxAllowed(null, empty), true);
+  });
+
+  it("requires membership when allowlist is set", () => {
+    const allow = parseWatcherMailboxes("eleven16th@gmail.com");
+    assert.equal(
+      isWatcherMailboxAllowed("eleven16th@gmail.com", allow),
+      true,
+    );
+    assert.equal(
+      isWatcherMailboxAllowed("Eleven16th@Gmail.com", allow),
+      true,
+    );
+    assert.equal(isWatcherMailboxAllowed("other@gmail.com", allow), false);
+    assert.equal(isWatcherMailboxAllowed(null, allow), false);
+  });
+});