The inability to receive email and being able to send email is usually caused by one of three issues:
1. Incorrect Incoming Mail Server Settings - This can be corrected by reconfiguring your email client settings with the correct information | Incoming and Outgoing Mail Server Information
2. Disk quota - Should you reach your maximum disk size quota, your incoming mail will not be processed. Log in to cPanel and check the general information sidebar for the current disk size that's being used. If it is at the maximum capacity, you may need to upgrade | Upgrade or Downgrade Hosting Plan
3. Archiving rules or aggressive spam rules - If you have aggressive spam rules in cPanel the email may be marked as spam and delivered to the default cPanel account instead. To check this, go to cPanel > Email Accounts, and Check Email for the default account with your cPanel username. If the emails are there, the spam filters may be too aggressive. You can lower them by going to cPanel > Spam Filters, and Configure Spam Box Settings. You should also review your archiving and organization rules in your email client.