Thanks - we're using Office 2003 so the bug should have been fixed
(according to that link) but there's some useful info in there.

On Jun 12, 7:34 pm, bstrum wrote:
We encountered this problem when rolloing out our addin. The code at the
following url fixed it for us.

http://support.microsoft.com/kb/830519

Benjamin Strum
ThinkTron Corporation

" wrote:
I've written an Outlook add-in in VS.net 2005, which when a user sends
an email it pops up a custom dialog. There are several buttons on the
form, one of which is a cancel button. If the user pushes the cancel
button then the dialog closes and it should cancel sending the email
(i.e., present them back to their message). The way I am doing this is
by setting the cancel variable (passed in ByRef to OnItemSend which is
handling ItemSend event) which should cancel the sending.

I've verified that if the cancel button is pushed then the cancel var
is being set to true but unfortunately the email is still sent
regardless.

Can anyone think of what might be causing this? Please let me know if
you need any more info.

Matt