Though you are sure you have set up your email channels and categories right, you would still want to ensure that you do not miss any of the customer emails.
To achieve this, go to Main menu >> Channels >> Fallback Settings(tab) and enable the default incoming category toggle as shown below.
Once you have enabled, provide a fallback category to which these tickets should be bucketed.
Question: When does an email fall into this fallback category?
Here are a few scenarios when emails might land up in the fallback category
Mails sent to the email id that has a forwarding rule set up but is not associated with any of the email categories.
Emails that are directly sent to the Happyfox forwarding address.