NGINX Cookbook

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As SMTP can run on multiple ports, we need to tell NGINX to load balance these ports as well. To do this, we simply define multiple listen lines within the server block:

server { 
    listen 25; 
    listen 485; 
    listen 581; 
    proxy_pass smtppool; 
    access_log  /var/log/nginx/smtp-access.log smtplog; 
} 

With the server port (named $server_port) logged in our custom log format, we're still able to trace issues down to a specific port.