I'd rather buy a bucket of old nun's spit...
I hope these 3 million people who's email addresses you are being supplied are all "opt-in" and it isn't just 3 million harvested emails? You could end up being one of the internet's lowest lifeforms
THE SPAMMER
Even if these people are all opt-in, what is to say that they will want whatever you plan on trying to sell them? Do your homework, target your customers and save your money for a properly organised advertising campaign.