I am implementing a split DNS setup where you have the external and internal domain example.com, and internally the same names resolve as external, but resolve internal addresses. This is useful for redirecting web pages to work with the same addresses both internally and externally, as well as internal and external emails. So far so good.
However, I have a slightly more complicated requirement when I would like to resolve names that are known to the internal DNS, but forward names that are not known to the external DNS (forwarding). So mail.example.com is known to the internal DNS and resolves, but smtp.example.com does not send this request to the external DNS forwarding. I really would not want to duplicate external DNS records in the internal DNS system, but this is problematic because the internal DNS must be authoritative for the domain inside.
Does anyone know how I can do this, preferably with BIND? I can not do anything with the transfer of a subordinate zone and, as a result, due to restrictions.
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