I am not in charge of the network, but I have responsibility for the Email Server at my workplace. We outsource networking, and how it was set is like this:
Mail Server (192.168.0.2)
Internet Firewall (155.x.y.z)
Internal DNS Server (mail.example.com -> 192.168.0.2)
Public DNS (World) (mail.example.com -> 155.x.y.z)
If i ping 155.x.y.z from within my LAN 192.168.0.0/24, I do not get a reply. When I consulted my network team, they said that I was not able to access 155.x.y.z from within the 192.168.0.0/24.
Problem My users use laptops, when they come into the LAN, for a while they still have (mail.example.com -> 155.x.y.z) in their DNS cache, and thus cannot get any reply from the mail server.
The options I have used are using a shorter TTL, but it has not worked because some of it is being overridden.
How can I fix the above?
ipconfig /flushdns
cmd
daily.