Have you set up any email addresses through cpanel yet?
If not it would be your_cpanel_username_@your_tch-hosted_domain.com which I would strongly recommend not to use.
Instead log in to cpanel:
click the email icon and set up real email accounts,
then click "default address" (in the email section), set the default address to :fail: (note the colons).
Then finally still in email section click "Spamassassin" and enable it.
If you want, enable spam box (in spamassassin section) but I would not recommend it.