I have a domain controller which is assigned as a primary DNS server to clients via DHCP (also on this server, Windows Server 2012). We have several servers that have both internal and external IP addresses, such as our file sever and our mail server. When client computers attempt to connect to these servers by their FQDN, they receive a DNS error. Pinging the FQDN on the affected machines reveals that they're attempting to access them via their external IP addresses, even though ipconfig /all shows they're using the DNS server.
Disconnecting and reconnecting to the network will cause them to start resolving successfully again for a while. I don't have any conditional forwarders set up on the DNS server.
Any idea what's going on here?