When an email address is blocked like this any email messages from the sender will go to that user’s junk email folder.
This list is also accessible in Outlook Web App, by navigating to the Options (by clicking the gear icon in the top right) and looking in the “block and allow” section. When a mailbox user blocks a sender the sender’s email address is added to the “Blocked Senders” list, visible in Outlook’s Junk Email Options. Mailbox users can set their own Junk email controls using Outlook or Outlook Web App, including blocking senders.