Just set up the 2820 and all seemed to be working well but have discovered that when a PC sends an email and it happens to go out via WAN2 (virgin) its blocked by them - fine going out via WAN1 (BT). What is the best way to ensure any PC sends mail via WAN1? but can use both WAN for all other traffic

Do BT have an authenticated SMTP Server ?

you'll need to make a load balance rule so that SMTP traffic always goes out through WAN1 - to go that go to WAN - Load balance policy and on there click an unused index number / link
For the setup of that rule - set Protocol to TCP, connection to WAN1, under Dest Port Start put 25 then click OK on there.
That should then work

Great thanks for your help