Outlook intermittent went using wireless

Hi I have a new Dell laptop which I connect via vpn to work network. When
using cable no problems but when wireless connection is enable Microsoft
outlook works for approx 10 seconds and then the open window becomes inactive
for 10 seconds, this continues thus only allowing you 10 seconds to write a
mail! If Wifi is switched off problem goes away but I somtimes I need the
wifi connection. Everything else works fine. Help!

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