Can not reach exchange server after changing IP address on SBS2003

More than likely the nat on your router/firewall needs to be updated with the new ip.

Other thing it could be is DNS.

When you try to connect are trying by IP or name?

did you change your mx record, sounds like it's pointing to your old IP.

Have you modified the DNS record that you point your iPad to, to the new IP Address?

Once you have done this, the iPad (airtime provider) will take about 24 hours to update their records, so be patient and it should work.

it seems mx record issue ... initially pint the dns name from internet...

or

log on to your DNS hosting console.. check the MX record pointing to your Exchange ?

and check the DNS is properly pointed /

for some more

u can

dig

www.mxtoolbox.com

The problem is that mails arrive at the server with POP3 and then redirected through exchange

your ipad still has to connect to the exchange server. you have the ipad connecting via your external ip that goes through your firewall and connects to your exchange server, if its not using a MX record then the ipad has the old external IP configured and you need to change this.

I have changed the IP adres in my Ipad to the IP adres I recieved from my provider. But when I want to check the connection the Ipad says that he can't controle the data I provided in my Ipad. And I am sure he is connected to the internet!

turn wireless off on the ipad, if you're on the network internal and you have wireless on its trying to resolve the external via the wireless internal, turn wireless off and it will be forced to go through the ipads carrier and use the external ip.  

Or go outside your network and check it from an external location.

check the DNS setting after adding the IP

ping the Gateway

Ping the dns

ping google.com

if get reply it could be ok

all the best