Does MyDNS support zone transfers?
Since MyDNS stores all its data in a MySQL databases, it is very simple to keep your secondary (and tertiary, etc) nameservers synchronized with your primary nameserver. Here are two suggestions:
1. Configure your slave nameservers to use the same database as the primary nameserver.
2. Use MySQL's replication capabilities.
If you absolutely must use DNS-based zone transfers, MyDNS supports outgoing AXFR by enabling the allow-axfr option, as well as incoming AXFR via the mydnsimport program.