I sent perhaps 100 or so emails out using a blind copy and I received a
reply from Systems Administrator with a very long list and each one stated "
Your message did not reach some or all of the intended recipients" and
"452.4.1.1. Too many recipients for message". I m guessing they are all on
that list.

Can someone advise approximately how many messages I can send at once with
the same message? And, should I resend these but break them up into smaller
groups?

Any help would be greatly appreciated. I have several thousand to send...