Are you saying that people who really and truly are not subscribed,
have never been subscribed, and have no interest in your list are
getting list mail from your list?

I'll assume that is what you are saying.  Ben Parker has indicated
suspicions about Hotmail itself, and that may be it.  However, reminds
me of a situation, oh, 'bout four years ago with one of my lists.

A bunch of people started getting our list mail.  These people were
not subscribed and sent many demands that we stop sending them this
junk (anything is junk if you haven't time for it and it is clogging
your mail system).  After a week of cajoling the victims I got them
to send me enough samples with full headers to find the one common
link which allowed me to trace it back to a guy in England.  He was
trying to establish himself as "the" medical info clearinghouse
and was just resending stuff from this that and the other list to
a list of people he had culled from various medical lists, primarily
people with "names" in the field.  With a few stern warnings, and
warnings to his ISP, we got this nonsense stopped.

Bad thing was he did it in such a manner for any given victim the
full header could have been construed as legit, indicating the
stuff truly was sent direct as possible from the list's host site.
I'm not sure I would have been able to figure it out if I hadn't
had the headers from a number of victims so I could isolate the
common oddity.

Douglas