Question: Our exchange server seems to conform to the requirements to get this working however it won't work. We do require that users re-authenticate every 10 minutes when using webmail, is this what could be causing the connection error?

As a side note the MfE connection wizard on the n900 is really poor, if your e-mail address contains an apostrophe, the wizard won't accept it but it won't bother telling you what the problem is, it just greys out the "next" button. Also not letting you save your settings unless you succesfully connect to exchange is pretty daft.