mail to hotmail addresses are going to junk

Hi,

I'm a member of IT support staff at a University in the UK.  We have been made aware that mail sent from our email domain to hotmail / windows live addresses are being sent to the recpients junk mail folder.  I have completed the following tasks:

•  I have review Sender Solutions web site at http://mail.live.com/mail/services.aspx#Section1 Sent an email to *** Email address is removed for privacy *** and have confirmed that messages sent from our email gateways are being filtered by recommendations of the SmartScreen® Filter.  No reason is given as to why?  
• Have verified that our SPF record is up todate
•  We have subscribed to the Junk Email Reporting Program.  We are waiting for our request to be processed.
• We have subscribed to  the “smart network data services” which show a historic view of mail sent to Hotmail addresses from each of our gateways including an indication in terms of a % of how many email are being sent to the junk folder.
•  We have used the Outlook Deliverability Support and this has confirmed again that mail from our gateways is being sent to junk folder
• I have reviewed information provide at Email Sender & Provider Coalition (http://espcoalition.org/index.php ) I have review document  at https://dub120.mail.live.com/mail/policies.aspx

All information that I have reviewed to date confirm that our gateways are marked by Smart Screen but provide no guidance on why mail from domain is going through to the junk mail folder.  It is unclear whether the reason why the mail is being junked is becuase of our mails servers , content of mail or are user's trashing mail.  If we knew the primary reason for mail being junked  we could start to tacle this issue. 

thanks,  Simon