[Enigmail] Expect signature header proposal

[Robert J. Hansen]

Eitan Adler wrote:
> No: I have defined the problem as: "Enigmail doesn't give effective
> warnings in the absence of an *expected* signature."

And, as people have told you several times so far, there is no known way
to convey an expectation of signature.  This makes your definition
nonsense: it's like saying "Enigmail doesn't magically summon unicorns."