A note from Spiceworks...
Disclosure: I work for Spiceworks (Hope I'm not intruding... found this thread from someone's Twitter)
Just a quick note to say that in the future, you might direct questions like this to the Spiceworks community first. Our support staff (and developers for that matter) are constantly scanning the forums there to help our users with whatever issues they're having.
To answer some of your questions here, we actually do use the Outlook Web Interface for communication with the Exchange server. It's the easiest way to get access to mail data in exchange without writing a native client. It's actually based on WebDAV and so pretty easy to integrate with.
Don't know if this is related, but one of the issues that we've been noticing since the 3.0 release is that some Exchange servers look for the username to be in the format "DOMAIN/username" while others expect "firstname.lastname@example.org". Many times, just the username (w/o domain will also work).
Hope this helps,