How can legitimate opt-in list publishers avoid
getting their mails caught in spam filters?
The key is to avoid getting your initial email caught in the
filter. Bayesian filters "learn" about spam characteristics
from the mail each user receives. Once a mail ends up in
the spam folder, all mails resembling it will be classified
as spam. Which means once you get in the spam folder, you
won't get out.
The opposite is also true, however. If the recipient discards
your email as ordinary trash, he thereby labels it as legit,
and mails resembing it will in future get past the filter.
So the key thing for the legitimate publisher is to avoid
getting that first email classified as spam. If you can get
the first email into the inbox, and the user doesn't mark
it as spam, you're in.
How do you do that? Avoid saying spammy things in that first
email. Sales pitches, for example. And even more importantly,
include words that only a legitimate sender would know, like
the first and last name of the subscriber. If your list, like
many lists, is related to some specific interest that the
subscriber has (model trains, for example), use terms related
to that field as well, because they will likely have occurred
in his legit email already.