Thank you for your posting. If you mean the drop down proxy access list available from the ‘From’ button on a composing message, no, I don’t believe it is possible to remove these entries. GroupWise does not provide any API to remove/disable this feature.
A large percentage of the information on this control comes from the proxy rights a user has granted to another user. You could remove/restrict this information using something like our Enterprise Proxy solution.
I hope this helps.