servo: persist the maildir

this way i don't lose my mail on every reboot...

wow i can't believe it took me this long to make the connection.

machines/servo/services/postfix.nix

@@ -20,6 +20,10 @@ in
     # TODO: mode? could be more granular
     { user = "opendkim"; group = "opendkim"; directory = "/var/lib/opendkim"; }
     { user = "root"; group = "root"; directory = "/var/lib/postfix"; }
+    { user = "root"; group = "root"; directory = "/var/spool/mail"; }
+    # *probably* don't need these dirs:
+    # "/var/lib/dhparams"          # https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/security/dhparams.nix
+    # "/var/lib/dovecot"
   ];
   services.postfix.enable = true;
   services.postfix.hostname = "mx.uninsane.org";

modules/impermanence.nix

@@ -68,8 +68,6 @@ in
         # "/var/lib/upower"            # historic charge data. unnecessary, but maybe used somewhere?
         #
         # servo additions:
-        # "/var/lib/dhparams"          # https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/security/dhparams.nix
-        # "/var/lib/dovecot"
       ] ++ cfg.service-dirs);
       files = [
         "/etc/machine-id"