Steve Atkins wrote:
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.
That matches my experience. However, rejection does not offer many
workarounds, because re-sending will likely repeat the failure,
while re-writing is something that apparently even spammers don't
want to do. Junk folders inspection can be solicited with a phone call.
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.
Yeah, complicated settings only work for geeks. Perhaps that's why
SPF, DKIM, or other anti-spam techniques' adoptions are snailing. In
addition, postmasters are a category of stranded people...