diff --git a/app/email_utils.py b/app/email_utils.py
index 912bfd3e..5230a6c0 100644
--- a/app/email_utils.py
+++ b/app/email_utils.py
@@ -742,8 +742,7 @@ def generate_reply_email(contact_email: str) -> str:
 
         # make sure contact_email can be ascii-encoded
         contact_email = convert_to_id(contact_email)
-        # remove potential space
-        contact_email = contact_email.replace(" ", "")
+        contact_email = contact_email.lower().strip().replace(" ", "")
         contact_email = contact_email[:45]
         contact_email = contact_email.replace("@", ".at.")
 
diff --git a/tests/test_email_utils.py b/tests/test_email_utils.py
index 8baa6d09..22ba32eb 100644
--- a/tests/test_email_utils.py
+++ b/tests/test_email_utils.py
@@ -404,7 +404,11 @@ def test_generate_reply_email(flask_client):
     assert reply_email.endswith(EMAIL_DOMAIN)
 
     reply_email = generate_reply_email("👌汉字@example.org")
-    assert reply_email.startswith("ra+YiZi.at.example.org+")
+    assert reply_email.startswith("ra+yizi.at.example.org+")
+
+    # make sure reply_email only contain lowercase
+    reply_email = generate_reply_email("TEST@example.org")
+    assert reply_email.startswith("ra+test.at.example.org")
 
 
 def test_get_addrs_from_header():