Q: When I forward an email message to a mailing list, the message is
   sometimes blank -- the headers are there, but no text.  I'm using
   Mozilla mail.


By default, Mozilla will forward a message as an "attachment", instead
of listing it "inline" as regular text.   Some mailing lists are set
to strip any attachments, or modify the message in such a way that
your mail client may no longer recognize the attachment.

Go to:

  Edit -> Preferences -> Mail -> Composition

In that pane, there should be a setting to forward message as an
attachment or inline.  Change it to "inline".