procedure TForm1.Button1Click(Sender: TObject);
var
 strEmail, strSubject, strBody, Param: string;
 begin
 strEmail := 'user@host.com';
 strSubject := 'Your Subject';
 strBody := 'Your Message Text';
 Param := 'mailto:' + strEmail + '?subject=' + strSubject + 

'&Body=' + strBody;
 ShellExecute(Form1.Handle, 'open', PChar(Param), nil, nil, 

SW_SHOWNORMAL);
 end;