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 hl-smtp02.viettelidc.com.vn is not the root of its zone.
Instead, try zone transfer on viettelidc.com.vn .
Instead, try zone transfer on viettelidc.com.vn .