OK, for VM you need to apply a fix.

 ftp://ftp.lsoft.com/listserv/beta-1.8d/fix2000b.hex

This contains the 2000b fixes and updates that include Attachments=
capability.  The UPD18D HEX file in the VM directory on the FTP site
is a base-level release and doesn't have Attachments= support.

This is per

 http://peach.ease.lsoft.com/scripts/wa.exe?A2=ind0101&L=lstsrv-l&P=R2952

from Eric, which stated:

>Date:         Fri, 26 Jan 2001 01:59:55 +0100
>Reply-To:     LISTSERV give-and-take forum <[log in to unmask]>
>Sender:       LISTSERV give-and-take forum <[log in to unmask]>
>From:         Eric Thomas <[log in to unmask]>
>Subject:      Re: What is the latest build of LISTSERV for VM?
>Comments: cc: [log in to unmask]
>Content-Type: text/plain; charset="iso-8859-1"
>
>There is now a FIX2000B HEX file on the FTP server in the beta
>directory. It is to be applied on top of 1.8d. Make a backup before!
>
>> Most specific question: Is the "Attachments=" list header keyword available
>> in LISTSERV (classic) on VM/ESA?
>
>Yes!
>
>  Eric