diff --git a/tests/channels/test_email_channel.py b/tests/channels/test_email_channel.py
index cb5aed45e..b6cea9263 100644
--- a/tests/channels/test_email_channel.py
+++ b/tests/channels/test_email_channel.py
@@ -1001,3 +1001,286 @@ def test_extract_attachments_sanitizes_filename(tmp_path, monkeypatch) -> None:
     saved_path = Path(items[0]["media"][0])
     # File must be inside the media dir, not escaped via path traversal
     assert saved_path.parent == tmp_path
+
+
+# ---------------------------------------------------------------------------
+# Agent-initiated file attachment tests (send with media)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_send_with_single_file_attachment(tmp_path, monkeypatch) -> None:
+    """Agent sends an email with a single file attached."""
+    sent_messages: list[EmailMessage] = []
+
+    class FakeSMTP:
+        def __init__(self, _host: str, _port: int, timeout: int = 30) -> None:
+            self.timeout = timeout
+
+        def __enter__(self):
+            return self
+
+        def __exit__(self, exc_type, exc, tb):
+            return False
+
+        def starttls(self, context=None):
+            return None
+
+        def login(self, _user: str, _pw: str):
+            return None
+
+        def send_message(self, msg: EmailMessage):
+            sent_messages.append(msg)
+
+    monkeypatch.setattr("nanobot.channels.email.smtplib.SMTP", lambda h, p, timeout=30: FakeSMTP(h, p, timeout=timeout))
+
+    # Create a real temp file to attach
+    attachment = tmp_path / "report.pdf"
+    attachment.write_bytes(b"%PDF-1.4 fake pdf content")
+
+    channel = EmailChannel(_make_config(), MessageBus())
+    await channel.send(
+        OutboundMessage(
+            channel="email",
+            chat_id="alice@example.com",
+            content="Please find the report attached.",
+            media=[str(attachment)],
+        )
+    )
+
+    assert len(sent_messages) == 1
+    sent = sent_messages[0]
+    assert sent["To"] == "alice@example.com"
+    assert sent.is_multipart(), "Email with attachment should be multipart"
+
+    # Walk parts to find the attachment
+    attachment_parts = []
+    for part in sent.walk():
+        if part.get_content_disposition() == "attachment":
+            attachment_parts.append(part)
+    assert len(attachment_parts) == 1
+    att = attachment_parts[0]
+    assert att.get_filename() == "report.pdf"
+    assert att.get_content_type() == "application/pdf"
+    assert att.get_payload(decode=True) == b"%PDF-1.4 fake pdf content"
+
+
+@pytest.mark.asyncio
+async def test_send_with_multiple_file_attachments(tmp_path, monkeypatch) -> None:
+    """Agent sends an email with multiple files attached."""
+    sent_messages: list[EmailMessage] = []
+
+    class FakeSMTP:
+        def __init__(self, _host: str, _port: int, timeout: int = 30) -> None:
+            self.timeout = timeout
+
+        def __enter__(self):
+            return self
+
+        def __exit__(self, exc_type, exc, tb):
+            return False
+
+        def starttls(self, context=None):
+            return None
+
+        def login(self, _user: str, _pw: str):
+            return None
+
+        def send_message(self, msg: EmailMessage):
+            sent_messages.append(msg)
+
+    monkeypatch.setattr("nanobot.channels.email.smtplib.SMTP", lambda h, p, timeout=30: FakeSMTP(h, p, timeout=timeout))
+
+    file1 = tmp_path / "doc.pdf"
+    file1.write_bytes(b"%PDF-1.4 doc")
+    file2 = tmp_path / "image.png"
+    file2.write_bytes(b"\x89PNG fake image")
+    file3 = tmp_path / "notes.txt"
+    file3.write_bytes(b"Hello, this is a text note.")
+
+    channel = EmailChannel(_make_config(), MessageBus())
+    await channel.send(
+        OutboundMessage(
+            channel="email",
+            chat_id="bob@example.com",
+            content="Multiple files attached.",
+            media=[str(file1), str(file2), str(file3)],
+        )
+    )
+
+    assert len(sent_messages) == 1
+    sent = sent_messages[0]
+    assert sent.is_multipart()
+
+    attachment_parts = []
+    for part in sent.walk():
+        if part.get_content_disposition() == "attachment":
+            attachment_parts.append(part)
+    assert len(attachment_parts) == 3
+
+    filenames = {p.get_filename() for p in attachment_parts}
+    assert filenames == {"doc.pdf", "image.png", "notes.txt"}
+
+
+@pytest.mark.asyncio
+async def test_send_skips_missing_attachment_file(tmp_path, monkeypatch) -> None:
+    """Non-existent attachment file is skipped without breaking the send."""
+    sent_messages: list[EmailMessage] = []
+
+    class FakeSMTP:
+        def __init__(self, _host: str, _port: int, timeout: int = 30) -> None:
+            self.timeout = timeout
+
+        def __enter__(self):
+            return self
+
+        def __exit__(self, exc_type, exc, tb):
+            return False
+
+        def starttls(self, context=None):
+            return None
+
+        def login(self, _user: str, _pw: str):
+            return None
+
+        def send_message(self, msg: EmailMessage):
+            sent_messages.append(msg)
+
+    monkeypatch.setattr("nanobot.channels.email.smtplib.SMTP", lambda h, p, timeout=30: FakeSMTP(h, p, timeout=timeout))
+
+    existing = tmp_path / "real.txt"
+    existing.write_text("I exist")
+
+    channel = EmailChannel(_make_config(), MessageBus())
+    await channel.send(
+        OutboundMessage(
+            channel="email",
+            chat_id="alice@example.com",
+            content="One attachment is missing.",
+            media=[
+                str(existing),
+                str(tmp_path / "nonexistent.pdf"),
+            ],
+        )
+    )
+
+    assert len(sent_messages) == 1
+    sent = sent_messages[0]
+    assert sent.is_multipart()
+
+    attachment_parts = []
+    for part in sent.walk():
+        if part.get_content_disposition() == "attachment":
+            attachment_parts.append(part)
+    # Only the existing file should be attached
+    assert len(attachment_parts) == 1
+    assert attachment_parts[0].get_filename() == "real.txt"
+
+
+@pytest.mark.asyncio
+async def test_send_with_unknown_mime_type_attachment(tmp_path, monkeypatch) -> None:
+    """File with unknown extension gets application/octet-stream MIME type."""
+    sent_messages: list[EmailMessage] = []
+
+    class FakeSMTP:
+        def __init__(self, _host: str, _port: int, timeout: int = 30) -> None:
+            self.timeout = timeout
+
+        def __enter__(self):
+            return self
+
+        def __exit__(self, exc_type, exc, tb):
+            return False
+
+        def starttls(self, context=None):
+            return None
+
+        def login(self, _user: str, _pw: str):
+            return None
+
+        def send_message(self, msg: EmailMessage):
+            sent_messages.append(msg)
+
+    monkeypatch.setattr("nanobot.channels.email.smtplib.SMTP", lambda h, p, timeout=30: FakeSMTP(h, p, timeout=timeout))
+
+    attachment = tmp_path / "data.unknown_ext_xyz"
+    attachment.write_bytes(b"some binary data")
+
+    channel = EmailChannel(_make_config(), MessageBus())
+    await channel.send(
+        OutboundMessage(
+            channel="email",
+            chat_id="alice@example.com",
+            content="Unknown MIME type.",
+            media=[str(attachment)],
+        )
+    )
+
+    assert len(sent_messages) == 1
+    sent = sent_messages[0]
+    assert sent.is_multipart()
+
+    attachment_parts = []
+    for part in sent.walk():
+        if part.get_content_disposition() == "attachment":
+            attachment_parts.append(part)
+    assert len(attachment_parts) == 1
+    att = attachment_parts[0]
+    assert att.get_content_type() == "application/octet-stream"
+    assert att.get_filename() == "data.unknown_ext_xyz"
+
+
+@pytest.mark.asyncio
+async def test_send_with_media_and_reply_subject_and_in_reply_to(tmp_path, monkeypatch) -> None:
+    """Attachments work together with reply subject and In-Reply-To headers."""
+    sent_messages: list[EmailMessage] = []
+
+    class FakeSMTP:
+        def __init__(self, _host: str, _port: int, timeout: int = 30) -> None:
+            self.timeout = timeout
+
+        def __enter__(self):
+            return self
+
+        def __exit__(self, exc_type, exc, tb):
+            return False
+
+        def starttls(self, context=None):
+            return None
+
+        def login(self, _user: str, _pw: str):
+            return None
+
+        def send_message(self, msg: EmailMessage):
+            sent_messages.append(msg)
+
+    monkeypatch.setattr("nanobot.channels.email.smtplib.SMTP", lambda h, p, timeout=30: FakeSMTP(h, p, timeout=timeout))
+
+    attachment = tmp_path / "summary.pdf"
+    attachment.write_bytes(b"%PDF-1.4 summary")
+
+    channel = EmailChannel(_make_config(), MessageBus())
+    channel._last_subject_by_chat["alice@example.com"] = "Original subject"
+    channel._last_message_id_by_chat["alice@example.com"] = "<orig@example.com>"
+
+    await channel.send(
+        OutboundMessage(
+            channel="email",
+            chat_id="alice@example.com",
+            content="Reply with attachment.",
+            media=[str(attachment)],
+        )
+    )
+
+    assert len(sent_messages) == 1
+    sent = sent_messages[0]
+    assert sent["Subject"] == "Re: Original subject"
+    assert sent["In-Reply-To"] == "<orig@example.com>"
+    assert sent["References"] == "<orig@example.com>"
+
+    attachment_parts = []
+    for part in sent.walk():
+        if part.get_content_disposition() == "attachment":
+            attachment_parts.append(part)
+    assert len(attachment_parts) == 1
+    assert attachment_parts[0].get_filename() == "summary.pdf"