Salesfully validates business and consumer email addresses, and offers a refund of the monthly subscription fee when incorrect information is provided. Unlike D&B Hoovers, Salesfully doesn’t continue to update information if it changes after your purchase, but does use a variety of public and proprietary databases to verify information on a regular basis.
As a last resort, you could try cold calling by phone. This is probably the most depressing and soul destroying activity on the planet. Even if you get past the usual questions such as ‘If you’re selling something – I’m not interested’ and ‘How did you get my number?’ you need a really slick and professional script and the ability to recognize and avoid lonely old ladies who just want to interact with someone, anyone, in fact.