BoltMail
How do I check to make sure that my contact lists have legitimate contacts?
The easiest way to make sure that your contacts are legitimate is to simply email them a conformation email. If they confirm then they are most likely legitimate and you can start emailing them.

You can then search your contacts an filter by unconfirmed that have been there for over 3-4 weeks and remove them if you wish to keep your lists cleaner.