This is my DNS configuration for the domain, there isn’t anything that might mark the domain as spam I think.
It’s similar to the DNS config on the first domain I added
mail.email.com is the FQDN and email.net is the domain I want to add
CNAME autoconfig.email.net mail.email.com 600
CNAME autodiscover.email.net mail.email.com 600
MX email.net mail.email.com 600 0
TXT dkim._domainkey.email.net v=DKIM1;k=rsa;t=s;s=email;p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAqZDiMCpzwgJb00o4FxiFOyRaQ/u9SISiY6XIvpLFlxyc0PGEIRcl2AGdqw7vfUTp5FIKupNDyzuXE4soBnAKoLgmGT7NjV49sDGraZqF7kHL0O0+5ljBLdcW+XPQ1kV3nrGpcfzMXdVRyPKMksvLSMzsu+jAO2akluBEY3AMqLyOq+fZnRUexcX4H9gBBkcQiff2r0LRm1LAJqmLBsXuajkihp9UNJyeBdOHpaw2w2pAzU7z140D7TJoVzQlwxbc1zD5wjkT8GqgmwY2tzz/Vm8AjMEaC79OmOj1CPFYBQDK0f+aEmBbH6SKIaxW3qDLrIAlRXtOhjgqrK0zXekU5QIDAQAB 600
TXT _dmarc.email.net v=DMARC1; p=none; rua=mailto:dmrac@email.com 600
TXT email.net v=spf1 a mx -all 600