To avoid spoofing of your own domains and these so-called CEO frauds and other variants, FuseMail suggests setup the following advanced policy.
1. Go to Policies > Data list and create a new data list called 'Permitted IPs'.
In this data list, you enter all the IPs which should be allowed to send on behalf of a customers domain incl. 3rd parties and the customers own IPs.
2. Create an advanced policy by going to Policies > Advanced policies > Create. Then the policy will have to look like this image below. For a bigger image, please click here.
Once this has been created, it will block spoofed e-mail. Just remember to keep the data list up to date yourself, otherwise the policy will catch false positives.
If you would like the users to be able to release the emails from the quarantine report, then don't forget to tick the box off saying 'Allow user access to quarantined messages' under the 'quarantine message'-action.