Since Confluence 3.5, it is possible to configure Confluence to send notifications from different names. It should provide the means to make the senders' addresses different too

All the notification emails I get come from the same address (per Confluence instance). For instance, all notifications from extranet come from extranet@atlassian.com

However, different emails will have different names associated with that email address, depending on who caused the notification to be sent.

This doesn't work at all for me. Gmail notices the first email, and uses the name associated with that address for all other emails from that address (at least in the same thread). Thus, when Some User comments on a thread, I get gmail telling me I have a new notification from Adifferent User - because he happened to be the author of the first notification email I got about that particular page.

A better way to do this would be to create an individual email address for each confluence user, using plus-addressing to make sure they all go back to the same place. For instance, notifications from Some User could be from "Some User <extranet+suser@atlassian.com>".

Any email replies would end up at the same place as if the address was just "extranet@atlassian.com", but Gmail (and other MUAs) would be able to correctly disambiguate which person sent which email.