By default, we have enabled SPAMBOX IMAP and webmail. You can check your spam at /spambox folder.
When you create a new email account, the /spambox IMAP folder will be created automatically after the first received spam. Only if you check your email using Squirrel or Roundcube Webmail, the /spambox IMAP folder will be shown after max 24 hour the first received spam. You can see it immediately after the first received spam if you subscribe the /imap folder .
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.