Here are some tips to stop spam in the first place, prevention rather than cure tips:
1. Don't use obvious, popular email addresses like sales@ info@. Spammers can easily find lists of new registered domains, and the first thing they will do is start spamming the popular email addresses at the new domains they find. Instead of sales use something less popular like thesalesteam.
2. Don't use catch all on emails (as brownie mentioned, i.e. receiving email sent to anyname@ your domain), just receive email on the addresses you have set up. And don't bounce back other emails as this adds to the spam congestion, and spammers don't use their own names as the from part, they use other normal people's addresses, so you will be bouncing back and spamming innocent people.
3. Don't make it easy for spam farms to extract email addresses from your website pages. Have a look at your contact us page, click on view source and search for @, if you can easily see email addresses then it is even easier for spam farm robots to automatically visit your page and extract them.
4. Don't display your email address in forum posts, again it is easy for spam farms to extract
5. Don't submit your website to directories where the directory displays your email address in an easily extractable format.
6. Don't get involved in forward email lists, ask your friends not to forward every joke or other type of forwarded message they receive, as this is a sure-fire way of getting your email address in more people's outlook as the email is passed on, and spammers nowadays also have spyware, malware, viruses, trojans to call upon to farm email addresses from outlook. The people who receive forwarded jokes, attachments are also more likely to have spyware etc on their PC via the attachments they open.
7. Make sure you have the lastest security updates on your PC to minimise the risk of having a virus or spyware used by spammers to get at your outlook email addresses.
If you are getting a lot of spam then chances are you have been lapse in one or more of these areas.
Prevention is always better than cure for spam, since once your email address is on the spam lists not only do you receive spam, but so will other people receive spam emails with your address as the from address (since spammers obviously don't use their real from address) so it will look like you are a spammer trying to send spam or viruses to people too. Also most cures either involve spam filtering which isn't foolproof and can mean that you lose important email too, or other mechanisms that force your potential clients to jump through hoops to send emails to you - which can be offputting and could lose you business.