If you're accessing your mail via the web, there's very little you can do.
If you're using a mail client (such as Outlook Express or Windows Mail) this (free) program will help:
http://www.mailwasher.net/
You can't be 'spammed' unless the sender of the mail either knows your email address or can guess at it.
With regard to the 'guessing' bit, spammers send out mail to, say,
[email protected],
[email protected],
[email protected],uk,
[email protected], etc, etc, in the knowledge that at least some of those addresses are likely to exist. (So, a Tiscali user, wanting to avoid spam, would do better to choose an email address such as
[email protected]. There's very little chance of a spammer guessing that address).
With regard to spammers 'knowing' your email address, it's always best to avoid using your 'main' address for signing up to web forums (or for internet purchases). It's far better to adopt a policy of using multiple addresses. See my post here for further information, and for a link to another post where I've provided details of a suitable provider (Gawab) for additional addresses:
http://www.theanswerbank.co.uk/Technology/Inte rnet/Question752662.html
Chris