I am using a proxy server on our LAN (AD/DHCP) -

Our proxy server used to have an IP of EG. 150.150.5.10 and was changed to
EG. 150.150.6.6

Now when I set up a Brand NEW workstation and log in to the network the IE
Proxy settings automatically default to the old IP 150.150.5.10 (Where does
IE get this IP from?)

If I change the IP manually to 150.150.6.6 everything works 100% BUT if a
different user logs in for the first time and a local account is created on
the same workstation IE once again automatically sets the Proxy IP to
150.150.5.10 for the new user.

Can I change the IP somewhere on my DC?