How to setup Active Sync for Exchange email to work on Mobile Devices

I've tried setting up exchange email on multiple android phones and have had no success so I've resorted to using touchdown. I'm currently trying to setup an ipad2 with exchange email and it's giving me "Cannot get Mail. The connection to the server failed.". When I setup the account it could not verify the user when all the info was correct. When setting up the touchdown app on the android phones, I use the same info and it works fine. After reading many post on this, I've checked and it seems everything is setup right on our server which is running exchange 2003 and I've opened up the correct ports on our firewall according to the posts, but it still doesn't work. I would like to get this working on the ipad2. I know it works because I've seen it setup on other people's ipads with there exchange server. Can someone give me the correct items to check so that I can make sure I have everything needed to get this working?