After reviewing the previous work on this topic from early July, I am
attempting to revive this discussion because we don't appear to have solved
it back then, and because I have new data.

In my case, a subscriber using Lotus Notes managed to get HTML through a
list with Language= NOHTML coded. I didn't even notice until he got worried
because his messages didn't pick up the list's top and bottom banners. (I
deleted the HTML versions when I went to NOHTML.) I have since taken a close
look at the MIME encoding for messages he sends.

With Lotus Notes, the MIME encoding seems to take place in something
identifying itself as a router. See Donna's original case, where the message
header included

  MIME-Version: 1.0
  X-Mailer: Lotus Notes Release 6.5.1 January 21, 2004
  X-MIMETrack: Serialize by Router on itsacr02a/serv/nottscc(Release
        6.5.5|November 30, 2005) at 02/07/2007 17:04:44
  Content-Type: multipart/mixed; boundary="=_mixed 0058420A8025730C_="

When the message consists of plaintext and HTML, the content type looks like

   Content-Type: multipart/alternative; boundary="=_alternative etc."

When the message consisted of plaintext, HTML, and an attachment (of a type
allowed by my list), we got

  Content-Type: multipart/mixed; boundary="=_mixed etc."

But in that case, the plaintext and HTML appear as a single part, with

  Content-Type: multipart/alternative; boundary="=_alternative etc."

so they are separated from each other by boundaries designated
"=_alternative etc." and from the attachment by boundaries marked with
"=_mixed etc."

Apparently ListServ only looked one level deep for HTML, finding only parts
labeled as an allowed type of attachment and as multipart/alternative; it
did not check the latter for an HTML part to be stripped.

This scenario does not entirely explain Donna's case. I believe that, if the
attachment sent to my list had not been an allowed type, it would have been
caught. But some similar nesting might explain how one got through her list,
and both odd behaviors came from subscribers sending out of a Lotus Notes
environment.

Donna, if you still want an answer and don't mind exposing the entire
message to someone from outside your list, I would be willing to scan a copy
of the whole thing for MIME structure. At least I now have an inkling what
to look for.

Hal Keen