Hi.
@julians1976, I think you’re asking about using Mail-in-a-Box’s built-in DNS server to set DNS records for subdomains so that subdomains resolve to a different server. Yes, you can set an A record for any subdomain or for any domain the box is hosting mail for (except the hostname of the box itself) to the IP address of the other server.
I think @paradoxbound is talking about how you might set up a second/alternate DNS server, but I don’t think that’s what you’re asking about.