expired or non-authoritative domains

[Konstantin N. Bezruchenko]

Hello,

I have a two DNS servers, which our customers uses to "host" their domains.

Sometimes customers forgot to renew domain, or just don't want to
renew it, or they move domain to other name servers.
However i still have records for this domains in my configs.

Is there any way to determine which domains are no longer use my name servers?

Sure, i can write some script just to make queries to root servers,
parse answers and look if domains is still refers to my nameservers,
but i believe there must be some native way?

Thanks.