Comment 12 for bug 3797

I think a footer is compulsory, at least as long as we let people subscribe other people. A custom header will be fine for filtering, but not for explaining. And a munged To: header cannot obviously distinguish between direct subscription, package/product subscription, bug contact, security contact, team membership, upstream forwarding, and other subscription types we might introduce later (such as Bugzilla-style watches).

It needn't be particularly complicated:
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