This package has no agent interface.
Reply any ticket notification and insert for example the following tag anywhere in the body of the mail:
<OTRS_CMD> close </OTRS_CMD>
Switch to the ticket from the ticket notification and compare the ticket state. The ticket should have the state closed.
The package restricts the functionality of this feature to agents known to the system, but it does not use advanced security mechanisms such as digital signatures and the like.