mastus: enable dovecot fts plugin

mastus/mail.nix

@@ -75,6 +75,27 @@
           group = postfix
         }
       }
+
+      # use mailPlugins.globally.enable after nixos 20.09
+      mail_plugins = fts fts_xapian
+
+      plugin {
+        plugin = fts fts_xapian
+
+        fts = xapian
+        fts_xapian = partial=2 full=20 attachments=0 verbose=0
+
+        fts_autoindex = yes
+        fts_enforced = yes
+
+        fts_autoindex_exclude = \Trash \spam
+      }
+
+      default_vsz_limit = 0
+
+      service indexer-worker {
+        vsz_limit = 0
+      }
     '';
     modules = [ (pkgs.callPackage ./fts_xapian.nix {}) ];
   };