MailerCheck is an efficient tool for bulk email list processing. It is fairly easy to implement with a basic csv file being all you need to get going. You can do partial lists, large lists, depends on how frequent you need to validate emails. Review collected by and hosted on G2.com.

For the price - it is missing a couple features that other services have. I also feel like it is invalidating a few more emails than other services. It has just basic categories for emails that have been checked, when it should have a few more like those emails that may bounce but worth a try. Review collected by and hosted on G2.com.