I would find this feature very useful: the ability for an administrator (and possibly other privileged users) to send an e-mail to everyone in a Confluence group.

For example, whenever I have to take the server down for upgrades, I can send an e-mail to confluence-user to let everyone know what's going on. And when it's back I can let them know again and point out new features they might try.

One way to do this is some page on the Admin console to type in a message to e-mail to the group members. Another is for Confluence to check a mailbox like JIRA does. That way it's as easy as mailing an address and it gets broadcast to the group members. This could later be extended to be a rudimentary mailing list system. If it were enhanced to archive these messages, we might even be able to drop Mailman for Confluence.