You are concerned that outlook express is started before the internet is completely up?
Outlook is a application it has no knowledge of the state of the internet connection it will just try to use it and if it can't it complains. You really can't do much about this. You could I guess choose to not auto start outlook on boot and manually start it. You could then wait until the internet is up before you start it.
There are other autostart managers you can load rather than just using the one built into windows but is it worth the effort to install it.