Whenever you add new prospects to your Prospect.io account, whether you're doing it manually or using the Import feature, you can choose to have us verify the validity of the address according to the verification level you've set.
Each email verification costs 1 credit. Packs of credits can be purchased at any time according to your needs. These that are not part of your monthly subscription never expire.
Note: Prospects created through our Chrome Extension are automatically verified for free.