At present, this is not possible. On 30 May 2001, I sent an enhancement
request to L-Soft, with copies to this list and the LSTOWN-L list, asking
for the following change:

        The use of 'Language=NoHTML' in a list configuration should result
        in the rejection of a single part message with the content type of
        'text/html', accompanied by an error message to the sender of the
        message.

In a reply posted to the LSTOWN-L list, Liz Marr <[log in to unmask]> wrote:

        Perhaps that would be better served by making it something that the
        Attachements= line could filter out?  So that Attachments= No would
        consider text/HTML as "attachment" and then if you wanted to keep it,
        you can use the Filter option and put that "type" of attachment in
        the exceptions?

I am writing this from home and do not have access to the email archives on
my office workstation, and I do not recall whether anyone from L-Soft
responded to this request.

Even if this request were implemented, it would not guarantee the complete
elimination of HTML postings. Given the variety of quasi-valid MIME content
types that less-than-well-behaved email software might use on single-part
messages with embedded HTML, it would be virtually impossible to completely
eliminate HTML messages, except on a fully-moderated list.

See the list archives for the complete text of my message. See the LSTOWN-L
archives for Liz Marr's followup postings.

My message:
http://peach.ease.lsoft.com/scripts/wa.exe?A2=ind0105&L=lstsrv-l&P=R5031
or
http://peach.ease.lsoft.com/scripts/wa.exe?A2=ind0105&L=lstown-l&P=R5948

Followup from Liz Marr:
http://peach.ease.lsoft.com/scripts/wa.exe?A2=ind0105&L=lstown-l&D=0&P=21188

Steve Price <[log in to unmask]> wrote:
>
> Okay so by adding 'Language = NoHTML' to a list's headers I can strip
> multipart MIME messages of there text/html part if there is also a
> test/plain part.  So how do I go about disallowing HTML posts
> altogether?

--
Paul Russell
Senior Systems Administrator
University of Notre Dame