In order to reduce spam you can configure SpamAssassin.
1. Log into cPanel and select SpamAssassin option.
2. You need to enable it and configure more appropriate score for you.
0 – each incoming message will be marked as spam. 5 – default setting. 10 – any message with a score less then 10 or 10 will not be marked as spam.
3. Once you enable spam box, a spam folder is created. All spam messages will be stored there. From time to time you will need to clear it.
4. You can add abusive email addresses to black list through Apache SpamAssassin configuration.
Also, you can add specific email accounts to white list, so messages will not go to spam folder.