This source is known to forward email
Our data indicates SpamExperts supports full DMARC compliance.
Contact SpamExperts for DKIM setup.
Add 'include:spf.antispamcloud.com' to your SPF record. Be aware though - that pulls in several additional DNS-querying mechanisms that count towards your number of DNS lookups. You could contact SpamExperts to understand if you could use a smaller list of authorized entries.