Mail Proxy Error

Hi

I am using nginx mail proxy for Lotus Domino Server. Its working fine on LAN, but while accessing from WAN, the replication shows "Network Error:Buffer was too small".

The code i am using is here :

mail
{
auth_http localhost/auth.php;
server_name Server;
pop3_auth plain apop cram-md5;
pop3_capabilities "LAST" "TOP" "USER" "PIPELINING" "UIDL";
smtp_auth login plain cram-md5;
smtp_capabilities "SIZE 10485760" ENHANCEDSTATUSCODES 8BITMIME DSN;
xclient off;
proxy_buffer 64000k;
server {
listen 25;
protocol smtp;
proxy on;
}
server {
listen 1352;
protocol smtp;
proxy on;
}
}
Please help on this