Unfortunately the servers that are handling your email switch too often to keep track of the IPs involved.
To only accept messages from the SpamExpert filtering nodes you need to allow emails based on our delivery hostname "delivery.antispamcloud.com". This hostname contains all active delivery IP addresses. Alternatively you can allow traffic from any IP address with the PTR record *.antispamcloud.com.
Please make sure your firewall does not block port 53 TCP.
Alternatively if allowing emails based on hostname is not an option, you could change your destination mail server to listen on an alternative one, such as port 2525 instead of the default 25 . The special port can be set for delivery when editing the destination route for your domain.
For users of our the old bundled configuration it is possible to use the information below.
To make sure you don't filter anything coming from our platform (since it is already filtered anyway) you can whitelist our platform in your own spam filters. You can also configure your mailserver to accept only incoming mail connections from this range IP addresses.
Here are all the IP addresses of our SpamExperts environment.