diff --git a/static/js/emailInbox.js b/static/js/emailInbox.js
index 18f883a..2655b33 100644
--- a/static/js/emailInbox.js
+++ b/static/js/emailInbox.js
@@ -8,6 +8,7 @@ import sessionModule from './sessions.js';
 import { initEmailLibrary, openEmailLibrary, closeEmailLibrary, isOpen as isLibOpen, prewarmEmailLibrary } from './emailLibrary.js';
 import * as Modals from './modalManager.js';
 import { applyEdgeDock } from './modalSnap.js';
+import { buildReplyAllCc } from './emailLibrary/replyRecipients.js';
 
 const API_BASE = window.location.origin;
 const _acct = () => window.__odysseusActiveEmailAccount
@@ -696,17 +697,7 @@ async function _openEmail(em, itemEl, preloadedData = null, mode = 'reply') {
 
     if (mode === 'reply-all') {
       // Build reply-all: TO = original sender, CC = everyone else (To + Cc minus me)
-      const origTo = (data.to || '').split(',').map(s => s.trim()).filter(Boolean);
-      const origCc = (data.cc || '').split(',').map(s => s.trim()).filter(Boolean);
-      const allOthers = [...origTo, ...origCc]
-        .filter(addr => {
-          // Extract email from "Name <email@x>" or "email@x"
-          const match = addr.match(/<([^>]+)>/) || [null, addr];
-          return !match[1].toLowerCase().includes(myAddress);
-        });
-      if (allOthers.length > 0) {
-        ccAddresses = allOthers.join(', ');
-      }
+      ccAddresses = buildReplyAllCc(data, myAddress);
     } else if (mode === 'forward') {
       toAddress = '';
       subjectPrefix = 'Fwd: ';
diff --git a/static/js/emailLibrary.js b/static/js/emailLibrary.js
index 1d00582..e1a4fb6 100644
--- a/static/js/emailLibrary.js
+++ b/static/js/emailLibrary.js
@@ -492,6 +492,15 @@ function _libCacheWriteBack() {
 // Simple global rather than cross-module import to keep coupling minimal.
 function _publishActiveAccount() {
   try { window.__odysseusActiveEmailAccount = state._libAccountId || null; } catch (_) {}
+  // Publish the active account's own address so reply-all can exclude us from
+  // the recipient list. This global was read in emailInbox.js but never set.
+  try {
+    const accts = state._libAccounts || [];
+    const active = accts.find(a => a && a.id === state._libAccountId)
+      || accts.find(a => a && a.is_default)
+      || accts[0];
+    window._myEmailAddress = (active && (active.from_address || active.imap_user)) || '';
+  } catch (_) {}
 }
 
 export function initEmailLibrary(config) {
diff --git a/static/js/emailLibrary/replyRecipients.js b/static/js/emailLibrary/replyRecipients.js
new file mode 100644
index 0000000..89f0341
--- /dev/null
+++ b/static/js/emailLibrary/replyRecipients.js
@@ -0,0 +1,25 @@
+// static/js/emailLibrary/replyRecipients.js
+//
+// Pure helpers for building reply-all recipient lists. No DOM, no fetch,
+// no shared state — safe to import anywhere and to unit-test under node.
+
+// Extract the bare email from "Name <email@x>" or a plain "email@x".
+export function extractEmail(addr) {
+  const m = (addr || '').match(/<([^>]+)>/);
+  return (m ? m[1] : (addr || '')).trim().toLowerCase();
+}
+
+// Reply-all CC = everyone on the original To + Cc, minus ourselves, with the
+// original "Name <email>" form preserved.
+//
+// `myAddress` empty/unknown ⇒ no exclusion. Comparing by exact extracted email
+// (not a substring `includes`) is what fixes issue #360: an empty self address
+// made `"...".includes("")` true for every recipient, so reply-all dropped the
+// entire Cc list and kept only the original sender.
+export function buildReplyAllCc(data, myAddress) {
+  const me = (myAddress || '').toLowerCase();
+  const split = (s) => (s || '').split(',').map((x) => x.trim()).filter(Boolean);
+  return [...split(data && data.to), ...split(data && data.cc)]
+    .filter((addr) => !me || extractEmail(addr) !== me)
+    .join(', ');
+}
diff --git a/tests/test_reply_recipients_js.py b/tests/test_reply_recipients_js.py
new file mode 100644
index 0000000..77dcc97
--- /dev/null
+++ b/tests/test_reply_recipients_js.py
@@ -0,0 +1,53 @@
+"""Pin the pure reply-all recipient helpers in emailLibrary/replyRecipients.js.
+
+Driven through `node --input-type=module` so we exercise the real JS without a
+full Vitest/Jest setup (same approach as test_compare_js.py). Skips when `node`
+is not installed rather than failing.
+
+Regression for issue #360: reply-all dropped every Cc recipient when the user's
+own address was unknown, because the old filter used `includes("")` (always
+true) instead of an exact-email comparison.
+"""
+import json
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+_REPO = Path(__file__).resolve().parent.parent
+_HELPER = _REPO / "static" / "js" / "emailLibrary" / "replyRecipients.js"
+_HAS_NODE = shutil.which("node") is not None
+
+
+def _run(js: str) -> str:
+    proc = subprocess.run(
+        ["node", "--input-type=module"],
+        input=js, capture_output=True, text=True, cwd=str(_REPO), timeout=30,
+    )
+    assert proc.returncode == 0, proc.stderr
+    return proc.stdout.strip()
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_reply_all_keeps_cc_when_self_unknown():
+    data = {"to": "Alice <alice@x.com>, bob@x.com", "cc": "Carol <carol@x.com>"}
+    js = f"""
+    import {{ buildReplyAllCc }} from '{_HELPER.as_posix()}';
+    console.log(JSON.stringify(buildReplyAllCc({json.dumps(data)}, '')));
+    """
+    cc = json.loads(_run(js))
+    # Empty self address must NOT wipe everyone (the #360 bug).
+    assert cc == "Alice <alice@x.com>, bob@x.com, Carol <carol@x.com>"
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_reply_all_excludes_only_self_exactly():
+    data = {"to": "Me <me@x.com>, Alice <alice@x.com>", "cc": "bob@x.com"}
+    js = f"""
+    import {{ buildReplyAllCc }} from '{_HELPER.as_posix()}';
+    console.log(JSON.stringify(buildReplyAllCc({json.dumps(data)}, 'me@x.com')));
+    """
+    cc = json.loads(_run(js))
+    # Our own address is dropped; a substring-similar address is kept.
+    assert cc == "Alice <alice@x.com>, bob@x.com"