Changes since SOA version
IXFR is a zone transfer request that returns changes since a specific SOA version. Enter the SOA version to request changes since then.
Not an apex domain
The domain 5rf0t8t7htp041mnkqcngscol8fi20qd.smtp.dk is not the root of its zone.
Instead, try zone transfer on smtp.dk .
Instead, try zone transfer on smtp.dk .