diff --git a/email_handler.py b/email_handler.py
index 7595bb33..744572fb 100644
--- a/email_handler.py
+++ b/email_handler.py
@@ -2080,17 +2080,18 @@ def should_ignore(mail_from: str, rcpt_tos: List[str]) -> bool:
 
 
 def send_no_reply_response(mail_from: str, msg: Message):
-    user = User.get_by(email=mail_from)
-    if user:
-        send_email_at_most_times(
-            user,
-            ALERT_TO_NOREPLY,
-            user.email,
-            "Auto: {}".format(msg[headers.SUBJECT] or "No subject"),
-            render("transactional/noreply.text.jinja2"),
-        )
-    else:
+    mailbox = Mailbox.get_by(email=mail_from)
+    user = User.get(mailbox.user_id)
+    if not user:
         LOG.d("Unknown sender. Skipping reply from {}".format(NOREPLY))
+        return
+    send_email_at_most_times(
+        user,
+        ALERT_TO_NOREPLY,
+        user.email,
+        "Auto: {}".format(msg[headers.SUBJECT] or "No subject"),
+        render("transactional/noreply.text.jinja2"),
+    )
 
 
 def handle(envelope: Envelope, msg: Message) -> str: