The difficulty with this is that for every option you give to
individual subscribers, you are at least doubling the number of
different message files that must be generated and that affects
performance, both of LISTSERV and of the SMTP host that is doing the
mailing.

As it is, there are already 7 different header options. Each of these
require that LISTSERV produce 7 different mail files, one for each
header type. If in addition to that, each subscriber got the option
of filtering off the attachment or not, then we've doubled that to
14. If you give them the option of _which_ types of attachments
they're willing to receive, then it could get quite out of hand.

It would take a significant development effort to make that an
option. There are a lot of issues that would need to be worked out,
such as what if the owner says no and a subscriber says yes (gut
feeling says that the owner setting should be processed first and
then if there's anything left over to strip, the subscription
settings can choose to do extra stripping, but I have not studied all
aspects of the issue). What about digest subscribers? Do we do a
different digest for subscribers who want attachments filtered off?
Currently the attachment filtering is being done before LISTSERV
worries at all about subscribers -- if we added this option, the
entire attachment feature might need to be redesigned.

We are not averse to doing significant development effort -- and
hopefully the richness, robustness, and performance of LISTSERV is a
testament to that. However, we do have to pick and choose where we
concentrate that effort so that we are adding the features that will
be most useful to most customers, or at least laying the groundwork
for useful features to be added later.

I sympathize with the sentiment: I filter out attachments on the
discussion lists that I run, and I would prefer to have attachments
filtered on any lists that I am a subscriber to. But all in all,
compared to the features that we are working on for the next release,
this one does not seem like it would be worth the effort. If there is
a groundswell of demand for this feature, it might be worth
reevaluating.

What you are asking for is already doable today for one-way mailing
lists (newsletter-type lists) by using the DBMS and mail-merge
features: set up a subscriber database which includes the
subscriber's preferences, and then put conditional blocks in the
message, or send different versions of the newsletter to different
segments of the subscriber population. There are a number of email
newsletters that operate this way.

So where this feature is lacking is mostly in discussion lists. Even
there, it can be handled by using topics. If the list owner decides
to allow attachments on the list, and some subscribers do not want
attachments, then there can be a list rule that you have to use a
certain topic when sending attachments. That way those who do not
want attachments can just select not to receive that topic. As with
most discussion lists with topics, this relies on the subscribers
remembering to use the topic, so there will be times when attachments
go out to everyone. And of course, in the case of a virus, the poster
may not even know that there's an attachment. So it isn't a perfect
solution.

So, given that
1) there are partial solutions available,
2) it would entail a lot of development time, and
3) there does not seem to be a huge demand for this feature,
I don't think you will be seeing it any time soon.

Francoise