Methods to obtain all the A records of a domain?

[Vincent W.S. Tam]

Dear all,

We're using a BIND 8.2.3 server running under Debian GNU/Linux system. We
have already blocked domain transfer to limited hosts by adding this entry
to /etc/bind/named.conf:

options {
        ......
        allow-transfer { 127.0.0.1; specified-host1; specified-host2; };
        ......
}

However, we found that another ISP can still obtain all the A records of a
domain we was hosting, when one of our customer switch their DNS hosting to
another ISP. At least, what A records we have set seems goto that ISP
already.

Can anyone tell us is there other methods to obtain a domain's A records,
without using domain transfer? Or, it is impossible, they just simply
remembered what A records we have setup?

Thank you for your time!

Best Regards,
Vincent