Question : Exchange 2010 SMTP with IPhone and Mail Filter

We have an Exchange 2010 server with about 10 iphones.  Recently we have been having spammers send email to our network bypassing our mail filter.  We can setup a rule on our firewall that prohibits smtp connections but that would break our iphone users.  

I was wondering if other people have had this issue and waht they have done to get around it.  Hopefully what I wrote makes sense.  

Please let me know if I am mistaken about how Iphones send out.  

Thanks Again

Baiju

Answer : Exchange 2010 SMTP with IPhone and Mail Filter

In our enterprise we have our iphones connecting to a OWA server (webmail), that ensures that we can place SMTP incoming and outgoing restrictions on the firewall to only allow that protocol to and from messagelabs (who filter our email). The phones work fine going through OWA .. always seemed that by having separation that way it reduces security incidents.

How do you have your iphones configured, directly to the exchange server ? that uses different ports than 25 though ?