On Nov 29, 2009, at 12:40 AM, Alessandro Vesely wrote:
SA provides a certainty measure, and a server may make different decisions
according to that score. Possible actions may include:
* set message header (SA default, Authentication-Results),
* set IMAP keywords (either Junk or NonJunk for TB users),
* deliver normally,
* deliver to a Junk folder,
* reject with various levels of detail,
* drop or quarantine, and possibly even
* create a record for a class of of messages (based on envelope data) that
the recipient can whitelist using a web form.
Is there an obvious decision matrix? In particular, would reliability be
better if a server rejects messages with higher spam scores and delivers to a
Junk folder for medium-to-hight, or the other way around?
Depends on your goals, and on your user demographic. And your definitions.
I remember a study from a few years back that said that the majority of typical
(consumer or non-technical business) users will only look in a bulk folder for
about two weeks after they're first exposed to it. With that sort of user base
then you're more likely to lose wanted email if you deliver it to a bulk folder
than if you reject it, as 9 times in 10 delivery to bulk folder is
indistinguishable from silently discarding.
On the other hand, more sophisticated users (a small minority but the sort of
users who might handle role accounts, say) are used to the concept of bulk
folders, and have tools like full text search available to them so delivering
to a bulk folder may cause less loss of wanted email to those users. It'll
likely cause delivery of more unwanted email to their bulk folders, but they
have the MUA tools to deal with that tradeoff.
(Dealing with presentation of spam filtering decisions is a subset of the more
interesting general problem of assisting recipients in handling mail volume -
prioritization, tracking and so on).
Cheers,
Steve