[Mailman-Users] loss of messages with text attachment

Dear all,

The messages sent to our local mailman lists never arrive to the list
members if they have any kind of attachment even text/plain. But the
messages with text/plain attachments appear in the archive. The other
messages appear in the archive only after using unshunt.

The configuration of Content filtering is to enable filtering and
remove message attachments that does not match multipart/mixed,
text/plain .
Is there any other settings elsewhere that interfere with handling
message having attachments ?

Thank you any help or hint,

Jean