Go to inbox.
Left click on the little 2 person icon bottom left.
When the contact list is displayed, hover cursor over the contact you want to delete and tick the little box next to it on the left.
Choose delete in the task bar on the email page.
When you now tab back using the arrow pointing left again top left the contact will be out of your contacts list. However they can still email you and it appears in Junk Mail.
To stop them emailing you. Without opening an email, tick the box next to the notification of email by again hovering over the line, and choose block in the top task or action bar and confirm when asked to.