Perhaps changing your SEND value to editor (rather than owners) will do it?
Following is excerpted from LISTSERV TIPS and LISTKEYW MEMO. While the
TIPS says only the editor can send mail to the list, the MEMO indicates
that the owner can also. I'm not sure which is correct. Your SEND value
is neither; it's owners. And, your editor is "trobb".
- - - - - -
To set up an edited list, use the list keyword EDITOR= (net-
address1),(net-address2).... and the SEND= EDITOR. All mail sent to the
list will then be automatically forwarded to the first person listed in
the EDITOR keyword list. Only the editors (not the owners) are allowed
to mail directly to the list subscribers. Any editor can send to the
list, but only the first listed editor will receive submissions. Editors
receive submissions in mail messages. Make sure the Editor address is
NOT a file server, list server, mailer,etc. - that may result in a
mailing loop.
 
If you need more than one editor to receive all submissions, you may
create a separate (non-edited) list with just the editors subscribed.
then you can use this small list, editlist in the EDITOR keyword of the
edited list as follows:
     EDITOR=editlist,(editlist)
 
You may also use the keyword: EDITOR-HEADER= (default value YES) to
control whether mail sent to the editor includes some explanatory
prose preceding the message. This preface includes the ID of the
original sender and notifies the editor that s/he can forward the
submission to the list and the preface will automatically be removed.
If the list is merely moderated, you probably want this heading prose.
If it is digested, you probably don't.
 
*********************************
* Send= (access-level) | Editor *
*********************************
    Defines the category of users who can mail or send files to the list.
  Possibly puts the list under control of an editor. The default value is
  "Public". When the  list is controlled by an editor,  any file or piece
  of mail sent  to the list is  forwarded to the editor, who  is the only
  person (with the list owner) to be  able to actually mail or send files
  to  the list.  The network  address  of the  editor is  defined by  the
  "Editor=" keyword (see below).