The problem is  not so much the  speed at which you send  the messages as
the manner in  which sendmail processes messages going to  a lot of local
recipients.  The only  way to  avoid killing  sendmail is  to send  these
messages with  as small a  MAXBSMTP value  as possible. A  single message
sent with MAXBSMTP  set to the usual  value of 2500 (usual  for LSMTP) is
enough to kill  sendmail, no matter how slowly you  send it. One solution
is to  run a DISTRIBUTE-only LISTSERV  on the sendmail host,  this way it
can be configured to spoon-feed  the messages to sendmail with MAXBSMTP=5
or 1  or whatever you  want. A small value  of MAXBSMTP will  keep things
under control because  sendmail will become slower as  the load increases
and will  accept new  messages at a  reduced rate, and  you will  reach a
balance.

  Eric