M$ more or less killed MAPI access from all external programs to fix their virus/worm/trojan/whatever you wanna call em problems with one of their service packs. I forget which but it was irreversible, quite a while ago and you will almost certainly have installed it. They broke all sorts of MAPI dependent stuff and caused a lot of grief.

They call it 'trusted code control'. Definition of trusted == written by M$. Anyway, these days to use MAPI from ANY non M$ (ie external programs like VB or Perl OLE) requires special patches to Exchange, and you must be delevering all mail to Exchange mailboxes or OST or the patches don't work. We were using some PSTs so......

See http://www.microsoft.com/office/ork/xp/four/outg03.htm and Google for 'Microsoft breaks MAPI access with service pack' for all the gory details.

PS We gave up on trying to make it work and ported code to sending mail without using MAPI....