VPN prevents outlook "out of office" from working

[Xunil]

As per thread title, all of our sales staff connect through VPN tunnels (Smoothwall) to gain network access while out and about.

General file handling works fine when they are connected, but not one of them can set outlook to deliver an "out of office" response.

All other out of office responses work fine, but if conencted through VPN it just won't play ball.

Any ideas or suggestions would be very much appreciated.

Thanks in advance