You will need to access the advanced interface for the http://webmail.blacknight.com interface to be able to export contacts. However to do this you will need to install an add-on to the browser. You can find the add-on name and steps here
When in the advanced interface click the button, then on button and choose where you want to save the file.
It will save it in .csv file which is compatible with most of the other web mail clients, like our newer http://altmail.blacknight.com as well as Gmail and Microsoft Outlook.