Ian,

Thanks for clarifying the nature of the question. I had thought--and I think
some others did, too--that you were describing a situation that had already
arisen.

In general, I find that IF a subscriber's email service objects to the
content, it generally returns a notice to the sender. That should get you
either a notation on an error summary, or a copy of the notice itself,
depending on how your error handling is set up. The objection need not be to
an attachment--I've got a subscriber whose email defenses "bounce" a
plaintext message containing a URL reference to a ZIP file.

It's possible for a list to be configured so that one rejection of this type
will automatically remove the subscriber. But that sort of configuration is
generally a bad idea. I go entirely the other way with my lists: no
automatic removal ever happens, and when a subscribed address stops working,
I send personalized test messages before giving up. (I do set the
subscription to NOMAIL during my testing phase, so the error notices don't
get out of hand.)

How much personal effort you can put in probably depends on the size of your
list, but anything that drops subscribers on the basis of one rejected email
is probably too hair-trigger.

I gave up trying to maintain lists of allowed attachment types some years
ago. Users keep coming up with new file types we need to allow. Worse, the
same file type can be given a different MIME type description by different
mail clients. The standard is anything but standardized.

Furthermore, there's at least one highly generic MIME description that can
be applied to almost any attachment: the application/octetstream one. I have
no choice but to allow those, because many of my subscribers' mail clients
use it for Excel-format spreadsheets, and my users exchange those in the
course of basic participation in our activities. But it can also be used on
ZIP files--and usually IS used, if they're carrying viruses. Until Listserv
offers attachment filtering based on file extensions--which are what
actually determines what application processes the file at the receiving
system--we've really got no way to keep them out.

> A related concern is that some images that are embedded within emails (and
> subscribers contribute a lot of them, they're quite necessary for
> understanding the work subscribers perform) are actually processed as
> attachments at some stage in transmission.

I suspect ALL images sent by email are processed as attachments. That's how
content that isn't text gets represented by a text encoding so it can be
handled by email. All the cute little corporate logos and signature images
sent by some of my subscribers come through as attachments.

Hal Keen



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