The catchall mail service will allow a certain mailbox to collect all emails, sent to a given domain name, but addressed to a non-existing mailbox.
In order to enable or disable it, simply click on the icon () in the Catch-all column, next to the selected mailbox. This will enable (if the catch-all service was not activated) or disable (if the catch-all service was already activated) the catch-all service.
Additionally, you can also enable or disable the catch-all service from the right-click context menu for the selected email.
NOTE: catchall services cannot be activated for a mailbox with active forwarding. You will have to disable the forwarding for that mailbox, if you wish to use the catchall services.