use red color for warning

email_handler.py

@@ -726,7 +726,11 @@ def handle_forward(envelope, msg: Message, rcpt_to: str) -> List[Tuple[bool, str
         msg = add_header(
             msg,
             f"""This email failed anti-phishing checks when it’s received by SimpleLogin, be careful with its content.""",
-            f"""This email failed anti-phishing checks when it’s received by SimpleLogin, be careful with its content.""",
+            f"""
+<p style="color:red">
+    This email failed anti-phishing checks when it’s received by SimpleLogin, be careful with its content.
+</p>
+""",
         )
 
     ret = []