Email Marketing Software

We have never used mass email marketing before but are giving it very serious consideration now. We can get a company to do it for us or we can simply buy databases and an application and do it ourselves. But we’re wondering whether our ISP might get a bit annoyed if we send out millions of emails? Thanks
The application enables us to bypass our ISP’s SMTP server (if that helps?!)

What’s the best (preferably free) bulk email mailing software to use for sending out emails to thousands of contacts? I’m looking for something like phplist, but hopefully better.

I am interested in sending emails in bulks of 1 million to online companies(not individuals). I was recommended to a software called eudora. Can I send out emails in bulks this big with this software? If so how? If not is their any other software you would recommend that would do the same?

am interested in all softwares that can do this task effectively.they could be free or not
email

I need really working software to send bulk email where i can find it
please provide me the link

the software should be really working software
good business

I am not spamming. It is for 1000’s of real estate agents who have joined my website and want my newsletter.