+of 'G') to incorporate new mail into the notmuch database.
+
+If set to nil (the default), new mail is processed by invoking
+\"notmuch new\". Otherwise, this should be set to a string that
+gives the name of an external script that processes new mail. If
+set to the empty string, no command will be run.
+
+The external script could do any of the following depending on