Well, fortunately, you ask for an opinion - I've no idea what would be a correct answer!
Looking at a few email policies, they seem very much over the top to me. The only points that seem to me worth making are that for most practical purposes, email is to be treated in the same way as written correspondence, and that it is rather less secure and very easily broadcast.
There might be other policies that would be relevant to email, amongst other mechanisms, such as a press relations policy, or a council publications policy.
Perhaps if the council is providing computers for councillors, some further policies might be needed, but my inclination would be to keep them very simple. It is pretty obvious that the law shouldn't be broken and that communications should be courteous and so on.