My ISP, for example, blocks any group of more than 99 messages from going
out. And they don't allow exceptions, even though everyone to whom I'm
sending has subscribed to the little newsletter I want to send. The fix is
either to set up an Exchange server or to see what your ISP has in the way
of special (read more $$) programs for mass mailers. You can do it, it just
isn't available to the average user. Communigate Pro, by Stalker Software,
is one such program that will do what you want. Your ISP would have to be a
subscriber for you to use it. It's basically Listserv software but can be
used otherwise.