From within cPanel, you're able to restrict mail flow each way, and disable login rights entirely.
Once you're logged into cPanel, whether directly or via my.LEOPARD, you can amend these settings easily.
Search for "Email accounts" and click through, then click Manage for the Mailbox that you wish to amend.
From there, you'll be able to enable or disable the incoming and outgoing mail flows, and restrict logins.
Worried about security? Contact us and we can take a look at your email security posture.