How do I create an employee without an e-mail address?

You can create user in Staffomatic without an email address. You can learn how here..

To create an employee without an e-mail address, go to "Employees" in the menu. Then you will see a blue button on the right with "invite employee". If you click on it, you can also create employees without an e-mail address.

Another possibility would be to create subaddresses of your own e-mail address. This works as follows: name+1@example.com, name+2@example.com, name+3@example.com, etc. Instead of a number you can also use the name of the person.