Problem with exchange server configuration

Hi all,

my problem is simple:

I add my exchange account without any problem when I was connected to my office’s WIFI… in this case the address of our exchange server is:

but in case i’m out of my office the correct server addess is:

so when I’m not connected to my office’s wifi, emclient could not connect to the exchange server… so syncronization was impossible…cause emclient was searching for internal server…

there is a configuration to use the internal server while i’m in my office?
is it possible to automatically swicth to external server once i will go out of my office’s WIFI??

Thanks in advance for any answers.