How can i block someone from emailing me?

If you use Outlook express you could filter the messages from this "someone" Either use function "Block sender" or create filter to send mails from that person directly to specific folder or delete them. Almost all mail clients have such functions (mark as "spam" or filter mails in specific way) Even if you use web mail client you have such possibilities

It varies from email to email. Simply put just find the options or tools screen. Most likely somewhere in there. Usually is very simple from that point on. Hope this helps. Good Luck.