We have a new ISP and a new firewall device. The old setup was via an ISA Server (also DNS and PDC) with a 10.2 address. Exhange server (10.1 address) currently has its default gateway as 10.2.
Installed Meraki NSA to the new ISP. It is on the same subnet and its interal ip is 10.254. Web browsing is fine on all my clients after changing cliet default gateway to point to the new gateway 10.254. When I change the exchange server’s default gateway to 10.254 (and also update the A-Record/Mx Record with the new ISP external address) no mail flows in either direction.