Funnily enough I just got advised to join this forum because I've had this issue twice now this month. As it occurred around the same time (Tuesday morning), I wondered if Virgin were running some kind of new housekeeping process that's causing my issue. On both occasions I've gone through the phone help route and had my mailbox 'reset', whatever that means. Today, the assistant told me it was 'for security' and that I should reset my password every 2-3 months to prevent this, whatever it was, happening. As I hadn't heard that suggestion before, I asked him whether that was a new policy and users would be advised to do that or risk keep losing access. I'm still wondering if this is the case.
I use Thunderbird as my email client, although the inbox was unavailable from the Virgin web front end too. Any advice gratefully received.
Paul