Missing headers of postings

Hi there
Suddenly postings on our Mailman (2.1.5) list are missing headers, the mails sometimes arrive without any Information about the sender or the subject. The headers From and Reply-to and Subject are missing.
In addition I wanted to send a HTML-Email with an attachment: It wasn't displayed correctly, the display of the mail began with the following.
--===============0751753693== Content-Type: multipart/alternative; boundary=Apple-Mail-1-691538562
What could cause this, what can I do about it?
Below is the beginning of the original Mail including headers.
Thanks a lot for your help! Roland
X-Gmail-Received: 27ac530151bc134384510d30f1d7492a37200011 Delivered-To: roland.studer@gmail.com Received: by 10.70.60.15 with SMTP id i15cs679375wxa; Fri, 26 May 2006 06:30:41 -0700 (PDT) Received: by 10.49.57.4 with SMTP id j4mr198736nfk; Fri, 26 May 2006 06:30:41 -0700 (PDT) Return-Path: <fachschaft-bounces@devzone.ch> Received: from zion.devzone.ch (zion.devzone.ch [193.138.215.50]) by mx.gmail.com with ESMTP id l27si500890nfa.2006.05.26.06.30.40; Fri, 26 May 2006 06:30:41 -0700 (PDT) Received-SPF: pass (gmail.com: best guess record for domain of fachschaft-bounces@devzone.ch designates 193.138.215.50 as permitted sender) Date: Fri, 26 May 2006 06:30:41 -0700 (PDT) Message-Id: <44770301.1714ba69.2db1.ffffc6b8SMTPIN_ADDED@mx.gmail.com> X-devzone-MailScanner-Information: Please contact the ISP for more information X-devzone-MailScanner: Found to be clean X-devzone-MailScanner-From: fachschaft-bounces@devzone.ch
--===============0751753693== Content-Type: multipart/alternative; boundary=Apple-Mail-1-691538562
--Apple-Mail-1-691538562 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8; delsp=yes; format=flowed

Roland Studer wrote:
"Sometimes"? Not always?
This is due to the fact that the main "Content-Type: multipart/mixed" header is missing along with the From:, etc.
Does this happen only with a certain poster or posters, at random or always? I don't know how it could be Mailman. I suspect some issue with the incoming message.
-- Mark Sapiro <msapiro@value.net> The highway is for gamblers, San Francisco Bay Area, California better use your sense - B. Dylan

Roland Studer wrote:
"Sometimes"? Not always?
This is due to the fact that the main "Content-Type: multipart/mixed" header is missing along with the From:, etc.
Does this happen only with a certain poster or posters, at random or always? I don't know how it could be Mailman. I suspect some issue with the incoming message.
-- Mark Sapiro <msapiro@value.net> The highway is for gamblers, San Francisco Bay Area, California better use your sense - B. Dylan
participants (3)
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John W. Baxter
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Mark Sapiro
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Roland Studer