Restructure folders, add mail host

The entire file structure has been reorganised into stable and unstable
to separate deployments running on either channel. A `mail` host running
Simple Nix Mailserver has also been added for testing to see if it's a
good alternative to soverin as well as SMTP for other services.

stable/config/hosts/mail/services/mail.nix

@@ -0,0 +1,25 @@
+{ config, ... }:
+
+{
+  imports = [
+    (builtins.fetchTarball {
+      # Pick a commit from the branch you are interested in
+      url = "https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/archive/5675b122a947b40e551438df6a623efad19fd2e7/nixos-mailserver-5675b122a947b40e551438df6a623efad19fd2e7.tar.gz";
+      # And set its hash
+      sha256 = "1fwhb7a5v9c98nzhf3dyqf3a5ianqh7k50zizj8v5nmj3blxw4pi";
+    })
+  ];
+
+  mailserver = {
+    enable = true;
+    fqdn = "mail.graven.dev";
+    domains = [ "anarkafem.dev" ];
+
+    loginAccounts = {
+      "noreply@anarkafem.dev" = {
+        hashedPasswordFile = config.secrets.files.mail_noreply_anarkafem_dev.file;
+      };
+    };
+    certificateScheme = 3;
+  };
+}