When sending out most email Launchpad will include an X-Launchpad-Message-Rationale header which you can filter with.
The basic rationale headers are for the cases where you are directly related to a bug:
X-Launchpad-Message-Rationale: Assignee X-Launchpad-Message-Rationale: Subscriber
If you are related to a bug through a team, an @ notation is added:
X-Launchpad-Message-Rationale: Assignee @ubuntu-kernel-bugs X-Launchpad-Message-Rationale: Subscriber @ubuntu-core-dev
Bug Contacts and Registrants, which are implicitly subscribed to public bugs, have their own headers:
X-Launchpad-Message-Rationale: Bug Contact (mozilla-firefox in ubuntu) X-Launchpad-Message-Rationale: Registrant (kiwi)
This is combined with the @ notation when you are a member of a team who is bug contact:
X-Launchpad-Message-Rationale: Bug Contact (ubuntu) @ubuntu-bugs
If the notification was generated in a duplicate bug, we tack on a via string:
X-Launchpad-Message-Rationale: Assignee via Bug 1332
This one is worth explaining a bit further. Let's say this bugmail is for bug 2129; the header here means you are the assignee of "master bug" 1332, of which 2129 is a duplicate. You can use this header to filter away bug that you are receiving from duplicates of a bug you are subscribed to.