nginx 访问跳转到二级目录

如访问：http://www.xxx.net 跳转到 http://www.xxx.net/mail

server {
       listen       80;
       server_name  www.xxx.net;
       rewrite ^/$ /mail permanent;
       client_max_body_size    10m;
       location / {
                 proxy_pass http://webmail-server;
                 proxy_set_header Host $host;
                 proxy_set_header X-Real-IP $remote_addr;
                 proxy_set_header ForwardedFor$proxy_add_x_forwarded_for;
                }

        }
upstream webmail-server     {
              server 127.0.0.1:8090;
                 }