The default value for Global Permissions, Manage Group Filter Subscriptions is "jira-developers". The problem is that this means that any member of jira-developers can add "jira-users" as a group recipient of a filter subscription. If the filter results has 100 issues at approx 1KB text per issue and jira-users has 10K members, then JIRA is trying to send 1GB of email! Not surprisingly this causes JIRA to go to 100% cpu and become rather unresponsive for a long time. Long enough for my corporate customers' alarm systems to send them wake-up calls...

Solutions to this accidental denial of service that I can see:

1. Education - don't do that! Or warn about the expected effects.
2. Set a limit on the number of members of a group that will be emailed, and make that limit adjustable
3. Rate limit the email so that JIRA only tries to send the emails at a sustainable rate. Of course, the job may not finish before it is due again.

~Matt