The only option is to hack the Outlook UI to find the window handle of the
tree view control and directly access it.
MAPI store providers really have no say in what icon Outlook uses.

Dmitry Streblechenko (MVP)
http://www.dimastr.com/
OutlookSpy - Outlook, CDO
and MAPI Developer Tool

"Anyone for Coffee?" wrote in
message ...

Do you know what my options are for this then?

Do I need to implement my own MAPI store?