Recently I was contacted by a reputable company in the financial industry that had many email addresses of customers and prospects but had never used them. In this case, some email addresses were collected, with permission, over a span of two to five years!
The good news is that they captured permission when collecting the email addresses. The bad news? Since these addresses were never used or validated, and some are as old as five years, there is the likelihood that many of these email addresses might not be valid anymore.