MyDNS will allow zone transfers (via AXFR) if the configuration option
allow-axfr is true. This is recommended only if you have an
absolute need for DNS-based zone transfers, such as if your secondary
name server is running BIND.
MyDNS does not support incremental zone transfers (IXFR).
If you need to support DNS-based zone transfers,
you have to enable allow-tcp. (This is not true for BIND 9.)
You can specify IP access rules for DNS-based zone transfers by using
an optional column called xfer in the soa table.
See soa.xfer.