Ssl – iphones and exchange, what am I missing

I am trying to get iphones to play with our exchange 2010 server.

I have opened ports 25 and 993 on the firewall, and I can get the account to validate, but I cannot send or receive email from it.

The iphone is set to use Exchange settings. I am able to connect from my computer from outside the company into the OWA through the firewall.

I have not purchased an SSL cert. Is this what I'm missing?

Any suggestions?

edit:

I currently have the exchange server running in a DMZ, so my firewall is simply passing all traffic back to the exchange server. I can validate the account (so my server address, username and password are good), but it will not send or receive email. I'm only getting 'allowed' messages on the firewall, so it does not appear to be blocking anything. But still no sending or receiving. Is an SSL cert required for this? I verified that activesync is running on the exchange server.