Redmine

I have Redmine 1.2 and whit this plugin
I have modifies the line 16 in system_notification.rb adding a whitespace inside [], before this Redmine returns an error self.users = options[:users] || [ ]
and now work but if exist a invalid email or a gmail address Redmine returns an error (The following error occured while sending email notification: "550 <testpub@gg.es>, Recipient unknown". Check your configuration in config/configuration.yml.) and not send any email