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 mail2-gw2.it.chula.ac.th is not the root of its zone.
Instead, try zone transfer on it.chula.ac.th .
Instead, try zone transfer on it.chula.ac.th .