emails going into Spam folder on (Virgin) server - help! (Mac)

[elvislives]

Wondered why I hadn't had many emails recently and while checking the webmail at virgin I found that there were over 200 emails in the Spam folder that hadn't come through to the Mail account I use on my Mac. I hadn't set anything to ask it to do that and I've missed some discounts at Ocado as well as the mumsnet roundup, amongst other things.

Why did this happen and how do I stop it doing it again?