Backup MX / Domain spam filtering


I have two objectives.

  1. To use our interworx server as an MX Backup for client’s domains. I don’t see it working at the moment although i have set it to be the backup MX in the MX records. Will it work without aditional DNS config on interworx server?

  2. Slightly related - i want our interworx server to be the first mail server in the loop for certain domains, scan all the mail for spam and viruses and then send it off to the client’s email server. Is this possible?