Using HAProxy

HAProxy configuration

Add the following to your haproxy.conf

frontend ft_smtp
	bind 0.0.0.0:25
	mode tcp
	timeout client 3m
	log global
	option tcplog
	default_backend bk_smtp

backend bk_smtp
	mode tcp
	log global
	option tcplog
	timeout server 3m
	timeout connect 10s
	server guerrilla 127.0.0.1:2525 send-proxy

This will let HAProxy listen on Port 25 and forward the traffic to localhost Port 2525. For multiple backend servers adjust the server line in the backend config accordingly, e.g. for two backends:

	server guerrilla-1 192.168.1.1:2525 send-proxy
	server guerrilla-2 192.168.1.2:2525 send-proxy

go-guerrilla config

If using HAProxy with the default configuration (and up to version 1.6.5), every connecting will be greeted with

220 mail.test.de SMTP Guerrilla(v1.6.5-12-g13718a2) #1 (1) 2024-06-06T18:42:18+02:00
554 5.5.1 Unrecognized command

Since version 1.6.6 you can enable the PROXY mode within the config for every server. Add the line "proxyon" : true, to your server config. go-guerrilla will accept and parse the PROXY command and will set the RemoteIP given by the remote server.