We sell software by Internet
I’m assuming that your website is up, and keyword-targeted for your audience. That will help people who need you to find you.
For an email campaign the #1 thing you need is to avoid spamming your prospects. Ideally, you have a list of people who want to be contacted about your type of software (that’s the purpose of a sign up form on your website).
If you don’t have such a list, then you’ll need to avoid getting your emails blocked. Follow the ICANN guidelines (http://www.icann.org/faq/) to ensure you don’t get yourself in trouble.
Post relevant information on your software on the various blogs that your audience reads. That will help to generate some targeted traffic (and hopefully get people to opt-in to your email list).
Make your subject line short and to the point. Make your first sentence on who you’re targeting and why (Here are more tips)
Ideally, use contact manager software to measure your email bounce and open rates. Don’t send out all your emails all at once. Split test your emails to make the offer get more results.