One of the few new features Apple has been advertising for Mac OS X 10.6 “Snow Leopard” is support for Exchange's autodiscovery feature that I recently worked so hard to support. Unfortunately, it doesn't seem to actually work. Mail goes so far as to look up the SRV record and POST a query to the appropriate URL, but then it just ignores the configuration it receives, logging an error somewhere about a domain not matching. Maybe it works with some other implementations, I dunno, but I followed the spec well enough that Outlook (which I think we can all agree is the definitive reference implementation for this) works fine with my setup.
You'd think they would test these things. You'd also think they would document these things somewhere. You'd be wrong on both counts, although the iPhone OS Enterprise Deployment Guide does link to Microsoft's documentation. By the way, the iPhone doesn't work with autodiscovery either, although it may just not support SRV records. I've reported both issues to Apple; we'll see what happens.