We recently replaced an old 2003 server with a 2012 R2 one. The server is in the 192.168.100.x range. The previous server and the new server serve as a domain controller. For now our client is still getting their e-mail (an exchange 2010 server) from another server in the 192.168.6.x range. Since we don't have control over that exchange server our options were limited to adjust the hosts file on each client for outlook to detect the exchange server during configuration.
The problem now is when people connect to the wifi on their cellphones and tablets it won't find the e-mail server and their e-mail only works when they switch to 3G mode.
I've tried to adjust the DHCP by adding a second DNS server to it. This works when I put the 192.168.6.x as primary dns, but then most of the clients refuse to connect to the server in the 192.168.100.x range. Putting the 192.168.6.x as second dns in the DHCP does not work. I can ping the exchange server by IP.
They also seem to have the problem when connection to mail.company.com/owa internally. I can also not ping mail.company.com/owa internally.
Any other ideas?