diff --git a/gvsds/apps/gerp/views/mail.py b/gvsds/apps/gerp/views/mail.py
index eadd5cbf..f7cc621a 100644
--- a/gvsds/apps/gerp/views/mail.py
+++ b/gvsds/apps/gerp/views/mail.py
@@ -230,6 +230,8 @@ class MailApplyView(ELTAuthenticatedAPIView):
             return Response({'code': 1, 'msg': '邮箱名需为字母/数字/点/下划线/连字符，长度 3~63'}, status=400)
         if not _PASSWORD_RE.match(password):
             return Response({'code': 1, 'msg': '密码需 8~64 位且同时包含字母和数字'}, status=400)
+        # 统一小写：Stalwart 按小写规范化存储 principal，DB 记录必须与之一致，避免大小写变体重复/错配
+        mailbox_name = mailbox_name.lower()
 
         try:
             quota_mb = int(request.data.get('QuotaMB') or 1024)
@@ -293,7 +295,7 @@ class MailChangePasswordView(ELTAuthenticatedAPIView):
     permission_classes = [IsAuthenticated]
 
     def post(self, request):
-        mailbox_name = (request.data.get('MailboxName') or '').strip()
+        mailbox_name = (request.data.get('MailboxName') or '').strip().lower()
         queryset = UserMailbox.objects.filter(UserUUID=request.user, Status=1)
         mailbox = queryset.filter(MailboxName=mailbox_name).first() if mailbox_name else queryset.first()
         if mailbox is None:
@@ -410,7 +412,7 @@ class MailLoginView(ELTAuthenticatedAPIView):
     permission_classes = [IsAuthenticated]
 
     def post(self, request):
-        mailbox_name = (request.data.get('MailboxName') or '').strip()
+        mailbox_name = (request.data.get('MailboxName') or '').strip().lower()
         queryset = UserMailbox.objects.filter(UserUUID=request.user, Status=1)
         mailbox = queryset.filter(MailboxName=mailbox_name).first() if mailbox_name else queryset.first()
         if mailbox is None: