Hi AJA I've updated the filter as per instructions for the KB but when I test access I'm still receiving the error message about not being able to open the other mailbox. There was a problem opening your mailbox. You may have already signed in to Outlook Web App on a different browser tab. If so, close this tab and return to the other tab. If that doesn't work, you can try: - Closing your browser window and signing in again. - Deleting cookies from your browser and signing in again. Please could you confirm if any other settings need to be applied once the filter has been installed. We are using EX2010 SP2 Update 1, Juniper SA4500 FIPS 7.1R3 (build 18671) we have SSO configured so users are auto signed into OWA. Regards Tony ... View more