How can I block an Internet Subscriber from receiving messages

[symichau]

I would like to block Internet Subscribers from receiving messages from regular users using the option "forward message" by pressing 5 in their mailbox. Is there a way to block it ?

[wong34539]

Check if the "Enable Extended Absence Notifications check box" is checked -- This actually PREVENTS messages from being deposited into the user's Unity mailbox

[symichau]

Is this check box in Unity? if so, in the mailbox classes or Template ?