Whilst not in possesion of anythig like that kind of tech knowledge, I can only report my experience, which was to test the set up by switching off AVG, then Win firewall, then avh & win firewall & finally, disabling wpa on the router.
I suspected the router as it was the only change to the previously perfectly working system. I spoke to my hosts, 1&1 & they said nothing wrong thier end & I could logon to webmail & see messages that way, but given that the Belkin interface is so straight forward when compared to say Netgear or Sonicwall stuff, I'm left scratching my head.