External anti-spam gateway
We use an antispam gateway. The mails are transferred from a web hosting server to a different server and send from here, we are forwarding with Smarthost, this is not a problem. right?
Not a problem. This is one of the great CrossBox advantages - it does not change your current setup with any additional configs or alterations to the system's software, it just wraps around it.
With this approach, CrossBox works out of the box with many external spam filtering solutions: