Check with your "double dose" subscribers to see if they also receive
material, including your list, through a newsreader.
 
I have several subscribers who prefer a reader, but with my list set
to "send=private", they have to subscribe to post to the list.
 
Through advice received here,lstown-L, I advised those subscribers to
set their list subscriptions to "nomail" while they continued to receive
posts via their newsreader.  They could still send to travel-L, and no
double messages.
 
[Thanks to all for the advice when I needed it.]
 
Jim Schaefer, [shortly not to be] manager of Travel-L