Faking Gateway

[Jos Chrispijn]

I have two gateway ip's in my network:
G1 = 8/1m and G2=50/10m.
Server1 (S1) is connected to G1 and all network clients are connected to G2.
As I sometimes have a lot of ports to download, I thought, let's change 
the gateway address of S1 to G2. That really works regarding the FTP 
part, but regarding my mail it is not (logically I am now presenting a 
domain name that doesn't match its ip address as it is G2 instead of G1).

Is there a way of switching to the 'fast' gateway with ftp traffic only 
(like port updates and manual outward/inbound ftp requests) and have 
outbound email follow the (standard) G1)?

Kind regards,
Jos Chrispijn