Jim,
 
    What you  observed is mail  from a list  that whose owner  has set
Mail-via=  Distribute.  This  means that  mail sent  to server  A will
result in A sending  a DISTRIBUTE job being sent to  servers B, C, and
D, and single-address mail to those users closest to it.  A partitions
the readership into sets  which are best reached via B,  C, and D, and
then sends just  those readers to those servers.  When  B receives its
share, it repeats  the process, possibly forwarding some  readers to E
and F (A  understands that E and F  are further from it than  B, and B
had some readers anyway, so A let B handle the re-partitioning).  This
is controlled by  the PEERS NAMES and LINKSWT FILE  files on LISTSERV,
which Eric  maintains.  The  intent is  to limit  the number  of files
transiting a  specific link to as  few as possible.  I  agree with you
that, if  A has to send  to 3 users at  X (which is nearest  to A), it
would make sense to combine those into one file, but it doesn't, and I
don't feel a need to bash Eric  about it, since DISTRIBUTE does a nice
job of handling more distant nodes.
 
    On the  "Who else is  interested?" point,  you never really  had a
complete list anyway.  LISTSERV would send individual mail to users on
the local  system, and  gang-of-five mail  to remote  systems (1  to 5
users  per  mail  file,  to  reduce  header  length  (thus  increasing
readability)).  So there might be 9  users at YALEVM reading the list,
but you'll only know  about 5 or 4, depending on  which group you fall
into.
 
Ross Patterson
Rutgers University