Does anyone know if this affects Postini?

We've switched once already this month - our new office was assigned an IP by C&W business that is in the same block as thousands of Virgin home cable-modems, so we got blacklisted by Spamhaus and others. Management got quite twitchy so I moved all the outgoing email to go via our Postini account which was previously only filtering incoming. Don't fancy having to find a third option now.