If you don't have the latest version of the manuals you don't have this:

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| Attachments= Yes | No | allowed_content_types [,Filter] |
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LISTSERV 1.8d kits dated after 2 May 2000 include a list-owner-configurable
message attachment filter. This feature allows you to control the posting
of various types of MIME attachments (images, audio, etc.) to your lists.

The options are:

Attachments= Yes  All types of attachments are allowed to be posted to the
list (the default).  Note however that other configuration options may still
disallow the posting of certain attachments, and that "Attachments= Yes"
does not override them.  For instance, if you have "Language= NoHTML",
setting "Attachments= Yes" does not override the Language= setting.  Or if
you have "Sizelim=" set to a value that precludes a file of x number of
lines from being posted to the list, setting "Attachments= Yes" will not
override the Sizelim= setting if the message with its attachment exceeds
the number of lines specified by Sizelim=.

Attachments= No  All types of attachments are disallowed, other than plain
text (always allowed) and HTML text (which is controlled exculsively by the
"Language= NoHTML" keyword setting). With "Attachments= No", LISTSERV
rejects messages containing attachments and bounces them back to the poster.

Attachments= No,Filter Same as "Attachments= No", except that LISTSERV
simply removes the unwanted material from the message and processes it
instead of rejecting it out of hand. The removal of material is a silent
operation, ie, the poster is not notified that the attachment was discarded.

It is also possible to allow certain MIME types to be passed through to the
list while rejecting or filtering all others.  For instance,

Attachments= image,application/*msword

allows only the specified attachment types and rejects everything else. If
you don't want to reject messages that contain other types of attachments,
but just want to remove all other types of attachments, you add the ",Filter"
parameter at the end of the line--ie,

Attachments= image,application/*msword,Filter

This means, "Allow all image and application/*msword attachments, and strip
all other attachments".  Again, note that plain text ("Content-Type:
text/plain") is always allowed and does not need to be included in the list
of allowed attachment types.  Likewise, HTML text is controlled exclusively
by the "Language= NoHTML" keyword setting.  Other text subtypes are, however,
controlled by "Attachments=", so they need to be listed if you intend to
allow them.

Note carefully that simply coding something like "Attachments= image" will
not necessarily allow all image files through. This is highly dependent on
the client being used by the poster. For instance, if your client attaches
all binary files as "Content-Type= application/octet-stream", regardless of
whether a given binary is (for instance) an executable image, a Word file,
or a compressed archive, and  you send a JPEG to a list with "Attachments=
image" set in the header, it will be rejected since the image does not have
a "Content-Type: image" tag. Specifically this appears to be the case with
Eudora 3.x but may not be limited to that particular client.

Note also that attachments sent by Microsoft Outlook cannot be blocked by
LISTSERV as they do not follow MIME standards (at least not up to and
including Outlook 97; this writer has not installed Outlook 2000). Outlook
sends attachments as imbedded uuencoded files and does not use the MIME
Content-Type: header.

The rejection message sent by LISTSERV when ",Filter" is not specified is
found in the BAD_ATTACHMENT mail template form (see chapter 9 for information
on LISTSERV's mail templates). Note that the BAD_ATTACHMENT template form is
a linear template and as such does not allow text formatting commands to be
used.

The reason HTML text is not subject to "Attachments=" filtering is to allow
you to reject (bounce) messages with attachments, while silently suppressing
HTML text in multi-part messages which also contain a plain-text alternative.
Some mail programs send both HTML and plain-text versions of messages, and,
even if you do not want HTML text on your list, there is little point in
keeping out people who use it (who are often new to the Internet and aren't
aware that their mail programs are sending HTML text) when you can simply
remove the HTML part.  At the same time, you may want to reject postings
containing images out of hand, rather than removing the images and
continuing. The same applies to Exchange attachments, which are filtered by
default (see "Language= Exchange").