orgmode / emacs /msmtp on winxp

[Erwin Panen <erwinpanen@fastmail.fm>]

Hi,

I guess this is perhaps more emacs related but here goes:

I'm trying to get going with gnus.
My system is running XP.
I have msmtp installed and working. (tested using cli)
In emacs using eshell and issuing msmtp --v I get the correct output.

Versions:
Gnus 5.13
Emacs 23.2.1
msmtp 1.4.17

What goes wrong is this:
In emacs I issue M-x mail, fill in, and C-c C-c to send => this opens my 
Thunderbird client.

I've added the equivalent of these to .emacs and .gnus
-------------------------------------------------------------------
;; with Emacs 23.1, you have to set this explicitly (in MS Windows)
;; otherwise it tries to send through OS associated mail client
(setq message-send-mail-function 'message-send-mail-with-sendmail)
;; we substitute sendmail with msmtp
(setq sendmail-program "c:/gnu/bin/msmtp.exe")
;;need to tell msmtp which account we're using
(setq message-sendmail-extra-arguments '("-a" "anderson"))
;; you might want to set the following too
(setq mail-host-address "gmail.com")
(setq user-full-name "Anderson Guy")
(setq user-mail-address "sivaram.notthere@gmail.com")

What can I do to debug this behaviour?