Looking to send a bulk email, but not have it reported as spam.

Hey, I have recently compiled a email list conataining about 700 email address' of people we have worked with. However in some cases there are about 40-50 address' for the same company. The problem with this is that their server will report this as spamand consequently none of them will recieve it. When I asked a co-worker they mentioned they had heard something about 'Blind-Email' sending, but I am unsure what was meant by this. The director has said she is wiling to purchase software if needed to do this.

Thanks