 Getting Outlook working with self signed certs
This may be totally off base here but you can get at least one part of outlook working with a self signed cert by visiting the https site with IE and accepting the cert permanently when prompted. I do this all the time when configuring the Outlook client to work remotely over the HTTPS/RPC proxy. If you don't do this Outlook fails silently.
Now, looking up free-busy info may use a totally different mechanism but it's worth a try before you shell out the $$$ for a valid cert.
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