The Virgin email service is not a free service, it is paid for out of the subscription we pay each month. It was part of the package I signed up for when I started using Virgin. You may have changed the conditions of service, so it no longer offers all the features it originally did, but calling it a free add-on looks like a step towards getting rid of it altogether. I imagine it would first be dropped from the offering to new customers, and then, when the number of users drops below a certain level, removing it from the few, remaining users.
I understand that running email servers is expensive, and getting rid of the service would improve your margins, but why not offer a paid service, maybe with better features, such as being able to add new addresses?