feat(server/mail): adding mail configuration for enium mailing

- working but not with my current configuration...
- have to see how to fix the issues with the freebox (not allowed to
touch the port 25)

services/self_host/mail.nix

@@ -0,0 +1,42 @@
+{ config, pkgs, lib, ... }:
+
+let
+	cfg = config.service.selfhost.mail;
+in
+{
+	config = lib.mkIf cfg {
+		services.rspamd.enable = true;
+		mailserver = {
+			enable = true;
+			stateVersion = 3;
+			fqdn = "mail.enium.eu";
+			domains = [
+				"enium.eu"
+			];
+			loginAccounts = {
+				"no-reply@enium.eu" = {
+					hashedPasswordFile = "/root/mail-passwd.txt";
+				};
+			};
+			certificateScheme = "acme-nginx";
+		};
+
+		services = {
+			roundcube = {
+				enable = true;
+				hostName = "mail.enium.eu";
+				extraConfig = ''
+					$config['smtp_host'] = "tls://mail.enium.eu";
+					$config['smtp_user'] = "%u";
+					$config['smtp_pass'] = "%p";
+				'';
+			};
+			nginx = {
+				virtualHosts."mail.enium.eu" = {
+					forceSSL = true;
+					enableACME = true;
+				};
+			};
+		};
+	};
+}