SSL authentication for outgoing e-mail

["Tim Jenks" <tjenks@...]

I need to set up SSL on exchange 5.5 to authenticate our exchange server to
a 3rd party proxy server and send encrypted messages.
Can this be easily done?
Do I need to purchase a certificate?
Can it be implemented selectively (ie. for one recipient domain but not
another)?

Any help with answering these questions would be much appreciated.

Tim