Every setting related to your email address can be found in the Add/Edit Services Area of JoMail. The first step in removing an email account, is to open the Add/Edit Services area.
Open Add Services
Select and Delete the Address
In the pane on the left side of the window, select the email address that you would like to remove. Hit the Delete button. This service be removed from your service list. Please note that messages and folder related to that service will remain. Those will need to be deleted separately.