I am doing a targeted adv. product and need to email business prospects such as dentists, drs. etc. I know about Reference USA that you can access online from local libraries but they don't usually have email infor available in the SIC Any helpful direction is appreciated Rich R.
You will find there are companies that sell email addresses for different industry niches. I doubt there is such a thing as an "email directory" though and sending unsolicited emails will see you breach the spam rules and risk real world, financial penalties.
You won't find any free email directories on the web. Indeed as sarahk said there are companies that sell email addresses for different business categories. I'm using leadsdeposit.com for some while and got only good lists from them. There are many providers to choose from but before buying be sure to google them for bad reports.