If you – or your client – ever needs to verify that a set of emails are valid, Neverbounce is a useful tool.
I recently used it to validate a list of 2,700 emails. Simple to use.
I uploaded a CSV file and within a couple minutes Neverbounce tested them all and identified 21 emails that are no longer valid.
Cost: $40 buys you credits to test 5,000 emails.