Most instructors require that you communicate via your ONID email rather than through a private messaging system. OSU has a webmail client that provides basic funtions for webmail accounts, sending and receiving email, account settings, etc.
As with Blackboard, you will need to log in using your ONID username and password. Remember to just use your ONID username and not your full email address.
Login to webmail at https://webmail.oregonstate.edu/imp/login.php
If you would prefer to use an email client such as Outlook, Thunderbird or Mac Mail, please access the ONID email client configuration helpdoc for guidance.