diff --git a/mcp_email_server/emails/classic.py b/mcp_email_server/emails/classic.py
index 7c643cd..dc3ad37 100644
--- a/mcp_email_server/emails/classic.py
+++ b/mcp_email_server/emails/classic.py
@@ -343,8 +343,15 @@ async def _batch_fetch_headers(
         for i, item in enumerate(data):
             if not isinstance(item, bytes) or b"BODY[HEADER]" not in item:
                 continue
-            uid_match = re.search(rb"UID (\d+)", item)
-            if uid_match and i + 1 < len(data) and isinstance(data[i + 1], bytearray):
+            # aioimaplib returns FETCH response in 3 parts:
+            # i:   b'N FETCH (BODY[HEADER] {size}'  - contains BODY[HEADER]
+            # i+1: bytearray(...)                   - raw header content
+            # i+2: b' UID N)'                       - contains UID
+            if i + 2 >= len(data) or not isinstance(data[i + 1], bytearray):
+                continue
+            uid_item = data[i + 2] if isinstance(data[i + 2], bytes) else None
+            uid_match = re.search(rb"UID (\d+)", uid_item) if uid_item else None
+            if uid_match:
                 uid = uid_match.group(1).decode()
                 raw_headers = bytes(data[i + 1])
                 metadata = self._parse_headers(uid, raw_headers)
diff --git a/tests/test_classic_handler.py b/tests/test_classic_handler.py
index 3245a6a..ada6fad 100644
--- a/tests/test_classic_handler.py
+++ b/tests/test_classic_handler.py
@@ -457,13 +457,16 @@ async def test_batch_fetch_dates_parses_response(self, email_client):
     async def test_batch_fetch_headers_parses_response(self, email_client):
         """Test _batch_fetch_headers correctly parses IMAP BODY[HEADER] response."""
         mock_imap = AsyncMock()
-        # Simulate IMAP response format for BODY[HEADER]
+        # aioimaplib returns FETCH response in 3 parts:
+        # - BODY[HEADER] line (no UID)
+        # - header content as bytearray
+        # - UID line
         mock_imap.uid.return_value = (
             "OK",
             [
-                b"1 FETCH (UID 100 BODY[HEADER] {100}",
+                b"1 FETCH (BODY[HEADER] {100}",
                 bytearray(b"From: sender@example.com\r\nTo: recipient@example.com\r\nSubject: Test\r\n\r\n"),
-                b")",
+                b" UID 100)",
             ],
         )
 
diff --git a/tests/test_email_client.py b/tests/test_email_client.py
index 20343c5..58647b7 100644
--- a/tests/test_email_client.py
+++ b/tests/test_email_client.py
@@ -590,13 +590,17 @@ class TestBatchFetchHeaders:
     async def test_batch_fetch_headers_parses_imap_response(self, email_client):
         """Test that _batch_fetch_headers correctly parses IMAP header responses."""
         mock_imap = AsyncMock()
+        # aioimaplib returns FETCH response in 3 parts:
+        # - BODY[HEADER] line (no UID)
+        # - header content as bytearray
+        # - UID line
         mock_imap.uid = AsyncMock(
             return_value=(
                 None,
                 [
-                    b"1 FETCH (UID 100 BODY[HEADER] {50}",
+                    b"1 FETCH (BODY[HEADER] {50}",
                     bytearray(b"From: a@test.com\r\nSubject: Test\r\n\r\n"),
-                    b")",
+                    b" UID 100)",
                     b"FETCH completed",
                 ],
             )
@@ -620,16 +624,17 @@ async def test_batch_fetch_headers_empty_input(self, email_client):
     async def test_batch_fetch_headers_preserves_uid_mapping(self, email_client):
         """Test that _batch_fetch_headers returns dict keyed by UID."""
         mock_imap = AsyncMock()
+        # aioimaplib returns each email as 3 items: BODY[HEADER] line, content, UID line
         mock_imap.uid = AsyncMock(
             return_value=(
                 None,
                 [
-                    b"1 FETCH (UID 100 BODY[HEADER] {50}",
+                    b"1 FETCH (BODY[HEADER] {50}",
                     bytearray(b"From: a@test.com\r\nSubject: First\r\n\r\n"),
-                    b")",
-                    b"2 FETCH (UID 200 BODY[HEADER] {50}",
+                    b" UID 100)",
+                    b"2 FETCH (BODY[HEADER] {50}",
                     bytearray(b"From: b@test.com\r\nSubject: Second\r\n\r\n"),
-                    b")",
+                    b" UID 200)",
                     b"FETCH completed",
                 ],
             )
@@ -640,3 +645,151 @@ async def test_batch_fetch_headers_preserves_uid_mapping(self, email_client):
         assert len(result) == 2
         assert result["100"]["subject"] == "First"
         assert result["200"]["subject"] == "Second"
+
+    @pytest.mark.asyncio
+    async def test_batch_fetch_headers_skips_non_bytes_items(self, email_client):
+        """Test that _batch_fetch_headers skips non-bytes items in response."""
+        mock_imap = AsyncMock()
+        mock_imap.uid = AsyncMock(
+            return_value=(
+                None,
+                [
+                    "not bytes",  # Should be skipped
+                    b"1 FETCH (BODY[HEADER] {50}",
+                    bytearray(b"From: a@test.com\r\nSubject: Test\r\n\r\n"),
+                    b" UID 100)",
+                ],
+            )
+        )
+
+        result = await email_client._batch_fetch_headers(mock_imap, ["100"])
+
+        assert "100" in result
+        assert result["100"]["subject"] == "Test"
+
+    @pytest.mark.asyncio
+    async def test_batch_fetch_headers_skips_items_without_body_header(self, email_client):
+        """Test that _batch_fetch_headers skips bytes without BODY[HEADER]."""
+        mock_imap = AsyncMock()
+        mock_imap.uid = AsyncMock(
+            return_value=(
+                None,
+                [
+                    b"some other data",  # No BODY[HEADER], should be skipped
+                    b"1 FETCH (BODY[HEADER] {50}",
+                    bytearray(b"From: a@test.com\r\nSubject: Test\r\n\r\n"),
+                    b" UID 100)",
+                ],
+            )
+        )
+
+        result = await email_client._batch_fetch_headers(mock_imap, ["100"])
+
+        assert "100" in result
+        assert result["100"]["subject"] == "Test"
+
+    @pytest.mark.asyncio
+    async def test_batch_fetch_headers_skips_truncated_response(self, email_client):
+        """Test that _batch_fetch_headers skips when i+2 >= len(data)."""
+        mock_imap = AsyncMock()
+        mock_imap.uid = AsyncMock(
+            return_value=(
+                None,
+                [
+                    b"1 FETCH (BODY[HEADER] {50}",
+                    bytearray(b"From: a@test.com\r\nSubject: Test\r\n\r\n"),
+                    # Missing UID line (i+2 doesn't exist)
+                ],
+            )
+        )
+
+        result = await email_client._batch_fetch_headers(mock_imap, ["100"])
+
+        # Should return empty dict since response is truncated
+        assert result == {}
+
+    @pytest.mark.asyncio
+    async def test_batch_fetch_headers_skips_non_bytearray_content(self, email_client):
+        """Test that _batch_fetch_headers skips when data[i+1] is not bytearray."""
+        mock_imap = AsyncMock()
+        mock_imap.uid = AsyncMock(
+            return_value=(
+                None,
+                [
+                    b"1 FETCH (BODY[HEADER] {50}",
+                    b"not a bytearray",  # Should be bytearray, not bytes
+                    b" UID 100)",
+                ],
+            )
+        )
+
+        result = await email_client._batch_fetch_headers(mock_imap, ["100"])
+
+        # Should return empty dict since content is not bytearray
+        assert result == {}
+
+    @pytest.mark.asyncio
+    async def test_batch_fetch_headers_skips_non_bytes_uid_item(self, email_client):
+        """Test that _batch_fetch_headers skips when data[i+2] is not bytes."""
+        mock_imap = AsyncMock()
+        mock_imap.uid = AsyncMock(
+            return_value=(
+                None,
+                [
+                    b"1 FETCH (BODY[HEADER] {50}",
+                    bytearray(b"From: a@test.com\r\nSubject: Test\r\n\r\n"),
+                    12345,  # Not bytes, should result in uid_item = None
+                ],
+            )
+        )
+
+        result = await email_client._batch_fetch_headers(mock_imap, ["100"])
+
+        # Should return empty dict since UID item is not bytes
+        assert result == {}
+
+    @pytest.mark.asyncio
+    async def test_batch_fetch_headers_skips_missing_uid_in_response(self, email_client):
+        """Test that _batch_fetch_headers skips when UID regex doesn't match."""
+        mock_imap = AsyncMock()
+        mock_imap.uid = AsyncMock(
+            return_value=(
+                None,
+                [
+                    b"1 FETCH (BODY[HEADER] {50}",
+                    bytearray(b"From: a@test.com\r\nSubject: Test\r\n\r\n"),
+                    b" NO_UID_HERE)",  # No UID in this line
+                ],
+            )
+        )
+
+        result = await email_client._batch_fetch_headers(mock_imap, ["100"])
+
+        # Should return empty dict since UID regex doesn't match
+        assert result == {}
+
+    @pytest.mark.asyncio
+    async def test_batch_fetch_headers_handles_mixed_valid_invalid(self, email_client):
+        """Test that _batch_fetch_headers processes valid items and skips invalid ones."""
+        mock_imap = AsyncMock()
+        mock_imap.uid = AsyncMock(
+            return_value=(
+                None,
+                [
+                    # Invalid: truncated (no UID line)
+                    b"1 FETCH (BODY[HEADER] {50}",
+                    bytearray(b"From: bad@test.com\r\nSubject: Bad\r\n\r\n"),
+                    # Valid email
+                    b"2 FETCH (BODY[HEADER] {50}",
+                    bytearray(b"From: good@test.com\r\nSubject: Good\r\n\r\n"),
+                    b" UID 200)",
+                ],
+            )
+        )
+
+        result = await email_client._batch_fetch_headers(mock_imap, ["100", "200"])
+
+        # Only the valid email should be in results
+        assert len(result) == 1
+        assert "200" in result
+        assert result["200"]["subject"] == "Good"