In the “Advanced Settings” Menu, you can specify a web proxy. You can choose the external mail server in “SMTP servers”. LUCY allows you to specify the server's address and port together with login information (if needed):
Note: LUCY comes with a built-in mail server. So it is not necessary to define an external mail relay!
If you want to use an external mail server please consult thу сhapter Mail Delivery Methods in LUCY