Mapi sendmail and Outlook Express

When I generate an email with MapiSendMail,  Outlook Express new mail dialog
box starts in modal mode.
Until the mail is sent completely, the control isnt returned to the origin
program.
This doesnt occur with other mail clients as Eudora.

I tried to create a session with MapiLogon first (although unnecessary) but
Outlook doesnt start.

res = MapiSendMail( 0, reinterpret_cast<unsigned int>(Application->Handle),
MapiMessage,

MAPI_DIALOG|MAPI_LOGON_UI|MAPI_NEW_SESSION, 0);

Any idea?

Thanks.