Sometimes customers see slow performance when accessing OWA over Dial-up and using SSL. Here are some things that you should check to make sure that you are getting the best performance.
Make sure that compression is enabled on the FE server. http://support.microsoft.com/?id=825371
Make sure that your firewall or proxy doesn’t require that every http connection require another SSL negotiation.
Check and see if the SSL conversion is hammering your CPU.
If it is, you might consider (in order of cost) a card that can offload the SSL load, upgrading your CPU, or load balancing with another FE. The SSL card makes the most sense in almost all scenarios.
The following options is not recommending that you turn off SSL!!! It just is pointing out that you can offload the SSL to a server infront of the FE servers in a DMZ. You can have the Exchange server in a DMZ with no outside access and a ISA server in front of it set to allow Anonymous connections:
Location: HKEY_LOCAL_MACHINE \ Software \ Microsoft \ Rpc \ RpcProxy \
Data type: REG_DWORD
value = 1
Then you could offload the first connection (SSL) to an ISA server or a third party SSL accelerator.