Marking as spam does not block a sender from emailing you. To add new email addresses to your blocked list, go to your Inbox, place a check in the box next to the email, then click the More actions icon. From the More actions drop-down menu, click Block sender. You can also create a Filter Rule to route the mail address into a specific folder.
That is a great question. I know how our inboxes can get full with Spam messages and stuff we just don't want. I'm here to help. I know that you can create or recreate the filtering rule that filtered those emails elsewhere. You will be asked if you would like to move those current messages in the inbox that apply to the new rule. That would get rid of the large number of emails not counted on the block list. I have provided a link to assist you.