Hello esgtomhodgson,
I wish I could really explain…. but I went into the server and found that one of my domains had email turned on when it should not have been. That was causing a conflict with my Google Apps email, which was why I was digging around in the first place!
Ever since correcting this I have been receiving notifications when a user posts a review. An added benefit, having having fixed the other problem I was experiencing that was unrelated.
Good luck!
Gillian