Is sending bulk mail from mail server feasible?

The business where I am working has a subscriber's list from our website, and paid a sufficient portion of change for an emailer program. The problem is, our list has near to 5 thousand individuals on it and growing. with gmail just allowing 100 emails for every account through on SMTP and I'm on a tight budget so I cant employ anybody else. I was thinking about doing a dedicated e-mail server off of the website server we have running in the workplace. Is it possible? to make e-mails on your own server, and then deliver it through your own SMTP? if it is, which software would I need to have and can I find any affordable or cost-free at least. We run a WAMP server, i set it up simply for information, but i could change it to lamp or whatever if demand be. Thanks a lot!