us4-smtp.usdev.wfsaas.net IXFR zone transfer

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 us4-smtp.usdev.wfsaas.net is not the root of its zone.
Instead, try zone transfer on wfsaas.net .