how can i block a particular email?

Depending on which ISP or email provider you are using, you may be able to filter out emails from a particular source on the server itself. I suggest that you visit the website and check what features are available. As for using such email clients as Microsoft Outlook or Outlook Express, you can select which senders you wish to mark as junk but they will simply be moved to a Junk folder or deleted on arrival. These programs do not have a facility to avoid downloading the email, only what to do with it once it arrives.

Put it in spam. mark spam.

which mail do you mean?

add that particular mail i.d. to your block list. I think that'll solve your problem.

U can mark them as spam or junk mails.. they'll be cleared automatically

there is no anti-spam system?