I realized the problem was related to my mail forwarding -- I have email
from 2 different non-Yahoo accounts/domains forwarded to my Yahoo account,
and when email was forwarded to me which carried an original address other
than my Yahoo "Reply to" address it was interpreted as Bulk Mail. I
presume this was an attempt by Yahoo to prevent mail spoofing.
I adjusted my filters for a while to send all mail forwarded from the
"rejected" email address directly to my Inbox. Now a week or so later I
note the problem seems to have been fixed and most of my mail is being
sorted appropriately without the filters.
Perhaps Yahoo has corrected this problem in their Bulk Mail algorithm. Or
alternatively, perhaps the week or so of using a filter to redirect all mail
to my Inbox gave enough "examples" or data points to the Bulk Mail processor
so that it will no longer classify mail as Bulk merely because it was
forwarded from my alternate email address.
Any other ideas?
Richard Kaplan, CFII