I suspect that the objectionable spam (in eye of beholder?) comes from
general lists, such as downloaded directories of all users at an ISP. I
get almost no spam to my business or CompuServe email addresses, and too
much to one at an ISP. It is difficult to get a mass address list from
CompuServe or my employer, trivial at my ISP.
I believe USENET postings are scanned for e-mail addresses. Sites
like Four11 and other people index sites can also be abused. I get
junk e-mail often at my UCI address.
Any good defenses?
Can't think of any that don't interfere with some intended uses of the
archives. One can delete the email addresses of the conversants (probably
not possible with stock MHonArc), but that makes it much harder for an
intended archive user to reply.
Excluding e-mail addresses can be done by specifying in message headers
that could contain e-mail address in the EXCS resource. However,
you will need to modify the source to exclude the printing
of the "<!--X-From: ... -->" comment at the start of a message page.
E-mail addresses within message bodies would require a modification
to the text/plain filter to mask those if desired.
I agree with Steve that doing this will hurt the effectiveness of
the archive for regular users.
A note to Achim, our list admin: you may have to watch out for junk
mail appearing on this list. I have seen other lists get infiltrated
by spammers. Hopefully you will not have to do it, but you may have to
restrict postings from subscribers only if the mhonarc list falls prey
like other lists have.