Reorganize handling of spam threshold scores and destiny mappings

[rjl]

Spam is unlike viruses/headers/attachments in that its diagnosis is score-based, not black-and-white. With that in mind, several different destinies may be applied to spam at different score thresholds:

* A = Tag threshold * B = Spam threshold * C = Quarantine threshold * D = Discard threshold

If score (X) is:

X < A : Ham, no tag, deliver
A <= X < B : Ham, tag, deliver
B <= X < C : Spam, tag, deliver
C <= X < D : Spam, tag, quarantine
D <= X : Spam, tag, discard

[dmorton]

a patch from Jacob Leaver [550] has this feature underway in a branch: branches/level4/trunk

[dmorton]

or try this link: source:branches/level4/trunk

I'm not sure what milestone to place this in, though.

[rjl]

Correction:

The conditionals should actually be as follows, to allow fall-through behaviour in the case of ties:

X < A : Ham, no tag, deliver
A <= X <= B : Ham, tag, deliver
B <= X <= C : Spam, tag, deliver
C <= X <= D : Spam, tag, quarantine
D <= X : Spam, tag, discard

Tie-breaking behaviour should also be described in the documentation, to make it clear to users how ties can be used to achieve a number of useful configurations.

[dmorton]

Done in stats branch, which will become Maia 1.1

[dmorton]

we have either the 4th level to work with in stats branch, Or Robert had

proposed NewThresholds