[Spambayes] Outlook plugin notes

[Tim Peters]

> * All outbound mail should be trained as ham

In connection with the Outlook client specifically, this one is especially
dubious:  Outlook doesn't use "normal" internet formats internally, and the
headers on outgoing mail *as saved in* Sent Items are especially sparse.
For example, this is the complete collection of headers on the last msg I
sent to Python-Dev, as it exists in my Sent Items folder:

"""
X-Exchange-Message: true
Subject: RE: [Python-Dev] Re: native code compiler? (or, OCaml vs. Python)
To: python-dev at python.org
"""

That's it.  No sender, date, from, errors-to, etc etc.  The *lack* of such
headers generates tokens in the default Outlook classifier, and if you don't
train on outgoing msgs they become good spam clues.

OTOH, if sent msgs were special-cased so that just the body got tokenized,
it might be helpful for people who get very few msgs.  But I expect that
anyone using email enough to feel burdened by spam probably also gets more
ham than they have time to deal with.  A better trick may be to make a point
of training-as-ham on received msgs that are *replied* to.