When sending out most email Launchpad will include an X-Launchpad-Message-Rationale header which you can filter with.

Bugmail

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.

Answer Tracker Mail

The basic rationale headers are for the cases where you are directly related to a question:

    X-Launchpad-Message-Rationale: Assignee
    X-Launchpad-Message-Rationale: Subscriber

The other possibility is when you are receiving the notification because you are an answer contact for the question's target:

    X-Launchpad-Message-Rationale: Answer Contact (mozilla-firefox in ubuntu)
    X-Launchpad-Message-Rationale: Answer Contact (Ubuntu)

This is combined with the @ notation when you are a member of a team who is an answer contact:

    X-Launchpad-Message-Rationale: Answer Contact (Launchpad) @launchpad-qa

Code Hosting Mail

Mail is only sent to subscribers of branches. If you are directly subscribed to a branch the rationale header is:

    X-Launchpad-Message-Rationale: Subscriber

This is combined with the @ notation when you are a member of a team who is subscribed to the branch:

    X-Launchpad-Message-Rationale: Subscriber @ubuntu-core-dev

Build Mail

Notifications regarding the various types of builds that Launchpad can perform for you have associated rationales. If you requested a source package recipe, live filesystem, or snap package build:

    X-Launchpad-Message-Rationale: Requester

If you created the source package (you are listed in its Changed-By field for a direct upload, or you requested a copy):

    X-Launchpad-Message-Rationale: Creator

If you did not create the source package but you signed it:

    X-Launchpad-Message-Rationale: Signer

If you did not create or sign the source package, but the build is in a PPA that you own:

    X-Launchpad-Message-Rationale: Owner

Any of these may have the @ notation appended if the relation is through a team, as above.