If you are up and running please ignore this.
This is how I think it should work, but It seems not to quite agree with some of the above.
I assume you have one VM media bill paying account. You have created a login using an independent email address. This login is used to log in to the Virginmedia home page where you manage the account, and also the Virginmedia webmail app. (mail.virginmedia.com, from memory)
You can access VM's email app either from your Viginmedia home page or directly from a browser. Once logged into the email app you need to add the email accounts separately using the actual email address and password you had previously. You should be able to add secondary email addresses with their password. Downside is everyone now knows the password to the admin account.
If you use a third party app such as outlook or google mail, then you do not need the new VMO2 login, just the actual email address you want to use.
This is how mine seems to work (but I cant reset my secondary account password) but many users are having problems.