Exchange 2010 RTM had RPC Encryption enabled on the Client Access Servers by default. This meant outlook 2003 clients needed to be configured to support MAPI Encryption by configuring the outlook profile.
In Exchange 2010 SP1 RPC Encryption is now disabled by default.
However if you upgrade an Exchange 2010 RTM server to Exchange 2010 SP1 RPC Encryption will remain enabled.
Only fresh installs of Exchange 2010 SP1 will have RPC Encryption disabled.