it-infra/m-labs-intl/nginx.conf

user www-data;
worker_processes auto;
pid /run/nginx.pid;
error_log /var/log/nginx/error.log;
include /etc/nginx/modules-enabled/*.conf;

events {
	worker_connections 768;
	# multi_accept on;
}

http {

	##
	# Basic Settings
	##

	sendfile on;
	tcp_nopush on;
	types_hash_max_size 2048;
	# server_tokens off;

	server_names_hash_bucket_size 64;
	# server_name_in_redirect off;

	include /etc/nginx/mime.types;
	default_type application/octet-stream;

	##
	# SSL Settings
	##

	ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3; # Dropping SSLv3, ref: POODLE
	ssl_prefer_server_ciphers on;

	##
	# Logging Settings
	##

	access_log /var/log/nginx/access.log;

	##
	# Gzip Settings
	##

	gzip on;

	# gzip_vary on;
	# gzip_proxied any;
	# gzip_comp_level 6;
	# gzip_buffers 16 8k;
	# gzip_http_version 1.1;
	gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;

	##
	# Virtual Host Configs
	##

	include /etc/nginx/conf.d/*.conf;
	include /etc/nginx/sites-enabled/*;
}


stream {
    # Upstream mail servers
    upstream smtp_backend {
        server mail.m-labs.hk:25;
    }

    upstream pop3_backend {
        server mail.m-labs.hk:110;
    }

    upstream imap_backend {
        server mail.m-labs.hk:143;
    }

    upstream smtps_backend {
        server mail.m-labs.hk:465;
    }

    upstream submission_backend {
        server mail.m-labs.hk:587;
    }

    upstream imaps_backend {
        server mail.m-labs.hk:993;
    }

    upstream pop3s_backend {
        server mail.m-labs.hk:995;
    }

    # SMTP
    server {
        listen 25;
        proxy_pass smtp_backend;
        proxy_protocol on;
    }

    # POP3
    server {
        listen 110;
        proxy_pass pop3_backend;
        proxy_protocol on;
    }

    # IMAP
    server {
        listen 143;
        proxy_pass imap_backend;
        proxy_protocol on;
    }

    # SMTPS (Secure SMTP)
    server {
        listen 465;
        proxy_pass smtps_backend;
        proxy_protocol on;
    }

    # Submission (Authenticated SMTP)
    server {
        listen 587;
        proxy_pass submission_backend;
        proxy_protocol on;
    }

    # IMAPS (Secure IMAP)
    server {
        listen 993;
        proxy_pass imaps_backend;
        proxy_protocol on;
    }

    # POP3S (Secure POP3)
    server {
        listen 995;
        proxy_pass pop3s_backend;
        proxy_protocol on;
    }
}