i advice you please don't do this because it is ****ming it doesn't make you money and you get trouble from your hosting account if they find that you are ****ming their hosting service they will bann your account.
i suggest you to build your email list using aweber.
I don't know about e-mail marketing software.I got a Express E-mail marketing service from the site TuckTail.com using which i had sent a bulk emails at a same time.Here they provide unlimited emails,easy email editor,Over 160 ready-made designs with email marketing service.
Wow, what you can do is google a mass email spammer. You can find email lists online for a large list, and send an email all at once (perfect for viruses and remote admin tools (DarkComet) if you're into that) but I've used it before, give it a shot.
Is this what you're talking about? Sending more than one email at once?