http://schemas.microsoft.com/mapi/proptag/x36e5001f (PR_DEF_MSG_CLASS)
if set, shows the default form to use. (Eg, IPM.Post, IPM.Appointment)

http://schemas.microsoft.com/mapi/proptag/x3fe20003 (PR_FOLDER_DESIGN_FLAGS)
is 1 if you can't post with the standard form


http://schemas.microsoft.com/mapi/proptag/x36df0102 (PR_WEBPAGE)
homepage info: 02 00 00 00 01 00 00 00 VV 00 00 00
               00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
               00 00 00 00 00 00 00 00 00 00 00 00
               LL LL LL LL
               URL
VV = 0x02 for non-default, 0x03 for default view
LL = LE32 length of URL including NUL
URL = NUL-terminated UTF16-LE URL
if URL gets erased, URL is replaced by just "00 00" (UTF16 NUL)