Thanks Ken, so the mask is supported even on the inspector for Outlook
2003? I know it works for the Explorer buttons.
Thanks

Ken Slovak - [MVP - Outlook] wrote:
Mask is supported for Outlook 2002 and later. It's only for Outlook 2000
that you need to use a workaround. Are you needing to support Outlook 2000?

The trick with Outlook 2000 is to use one color as a mask color, say
magenta. That color can only be used where you want masking. Then you do
some fancy stuff with the Win32 API and separate the mask and image and
pop them onto the clipboard and use PasteFace to add the button image.

See http://www.daveswebsite.com/articles.../default.shtml for a
C++ example and KB288771 for a VB example. Offhand I'm not familiar with
any C# examples but there may be some out there if you Google for
"PasteFace".