When I have at VPN connection open, I'm finding that Outlook refuses to send
any email out. How do I fix this (besides closing my VPN connection each
time I want to send/receive!)

As a side note:
I've noticed other gimpiness with it too relating to packet fragmentation,
where my mail would bounce for no reason. I had to change my MTU to fix
that. Why is Outlook seemingly so sensitive to network configuration?
Outlook Express does not seem to have these limitations. Is this some kind
of negative feature introduced with this version of the product? Should I
go back to my older version? I don't use most of the fancy features
anyways.