ANTI SPAM MEASURES :

"Catch All" default email addresses are wonderful collectors of spam. This is because they let any email through with the address (anything)@yourdomain.com.
Solution : DO NOT ACTIVATE THE CATCHALL OPTION

An easy and effective way to cut down spam is to specify forwarders or mailboxes.
This means that an email that is correctly address, specifically for you, is either forwarded to you ISP email address or held in your Mail Box on your server space.

All other emails that are incorrectly addressed to your domain can be then discarded.

The directions below apply to those servers that operate cPanel.

www.(yourdomain).com.au/cpanel

Login :

UserName: yourusername
PassWord: youruserpassword

Click on Mail

In Mail Manager Main Menu,
Ensure that you have a mail forwarder for each of your exact email addresses.
or
set up a POP3 Mailbox for each of your exact email addresses.

Click on Set default address
Enter :blackhole: to discard all incoming unrouted mail

This means that all incorrectly addresses emails (they constitute the bulk of spam) will be deleted whilst the correctly addressed emails will get through to you.
 

FURTHER MEASURES:

PRECHECKERS :

Obviously, changing an email address will stop spam  - especially if you do not use a common prefix like admin, support, info etc. This solution may not be convenient for businesses with a lot of contacts.

If you have a lot of spam coming in on an email address important to your work or business, you may have to use a prechecker

Click Here to read about Mail Washer

PREVENTATIVE

New websites should not have plain text email addresses displayed either on the page or in the coding of the page.  There are various java scripts and php scripts available to encode your email address.

If you have a spambot filling in your forms, you may need an image verification to prove that a human is trying to send information to you.

More Information here