I've looked for about 15 minutes searching around and haven't found the answer.
I'm rolling out JIRA at Siemens and two of my big sells are that we will reduce email traffic and kill the use of spreadsheets for managing workload.
Initially the system notifications to email are ok, but I'm left thinking why is there not a notifications space, facebook, twitter, etc... they rarely send you emails.
You spend time on the system and a little (1) pops up in the top and you can see someone has commented on something you're watching.
This is vital, surely you've thought of this already?