It's very much an overkill but you could set up a Yahoo! group to do this. Restrict the group options severely at the setup stage, and also make it a private group. The major immediate restriction is that you can only add the address's of ten people in any one day. So it's going to be a long process getting everyone 'on board'.
As I said, an overkill, but an option that could be looked at even if only to clarify choices in other areas.
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