bulk e-mail sending software

I have a homebased business and I get about 500
to 1000 e-mail address a day. I have been sending my business opportunity out one at a time.
If anyone knows of a free software program that
I can get to load up all my addresses and send them out all at one time please let me know. I have had an autoresponder before but it was to complicated to use. NEED HELP BADLY!!!!