The SpamExperts solution fully supports IPv6.
If the IPv6 addresses were not present at setup of your cluster, please provide the details to our support team to have them added to the configuration. Ensure your server hostname points to the primary A record (1) and includes all AAAA records (1 or more) for the IPv6 addresses.
We recommend that your domains always have at least 1 MX record without AAAA records for now to avoid compatibility issues with bad IPv6 senders.