The spambox@ plugin permits you to check rejected SPAM using imap or pop3.
Please note that all the SPAM messages older than 7 days , will be removed automatically from your account each day to avoid disk space problems.
Please click in the "Spambox" button in the "Spam and Virus protection (ASSP)" section at your cPanel for more information about how to activate it and use it.
You can also use it through Roundcube Webmail in cPanel.