Spam is a term used to mean unsolicited, bulk e-mail that clogs your e-mail inbox and is often annoying. A spam filter is a program that will actually capture e-mails that look like spam before they are sent to your in-box.
If you just want to stop it at the mailbox, you can do that by spam filter.
Anti-Spam EMail Filtering & Solutions
Shah Net works with POP, IMAP, Gmail and AOL to download your email before it is delivered to you, sort out the spam, and then just delivers the good mail to you. You can use CAPTCHA to verify senders, set up white lists for individual emails or entire domains, customize verification emails, download lists that include a week’s spam and more. The service is free for single email accounts that receive less than 1,000 spam messages a week. If you need to cover multiple accounts or have more spam than the free levels, you can pay for a premium account.