stream {
limit_conn_zone $binary_remote_addr zone=straddr:10m;

upstream backendsmtp {
server smtp1.local:25;
server smtp2.local:25;
}

server {
listen 2025 ssl;
error_log /logging/stream_local_smtp.log debug;
ssl_certificate /nginx/crts/sdom.cert;
ssl_certificate_key /nginx/crts/sdom.key;
include /nginx/conf/sslciphers.conf;
ssl_session_timeout 60m;
ssl_handshake_timeout 10s;
proxy_connect_timeout 10s;
proxy_timeout 300s;
proxy_pass backendsmtp;
limit_conn straddr 15;
limit_conn_log_level error;
}

}

---
nginx for Windows http://nginx-win.ecsds.eu/