[Bug 1094696] [NEW] Event notifications on postings

Public bug reported:

It looks like there is no way for a MM3 plugin to be signaled for a new posting.

It would be great if core could provide a notification to the plugins that have subscribed to this event when a new post occurs.

This notification should carry some interesting information, like the number of recipients and the message size.

This request is also essential for the MM3-Metrics module (https://launchpad.net/mm3-metrics).

** Affects: mailman Importance: Undecided Status: New

** Tags: events mailman3 metrics modules notification plugins post