Hunter.io is a tool which fully focusses on the email part of a business. You can do the following things with Hunter.io:
You found the companies you want to target? When filling out their domain name in Hunter it will give you back email addresses find on the web. Even though if your buying persona isn't in there it will give you valuable information as it reveals the email structure. Examples is; email@example.com.
Do you know exactly who you want to target? Maybe with the help of Linkedin Sales Navigator. Enter the first name, last name and the domain name and find the exact email of that person. This way you keep your high deliverability and know before hand it will land in his/her inbox. It leaves the guessing behind.
Do you have lots of email addresses you want to send an email to but you are unsure if they will actually arrive? Use the email verification to check the if the email is deliverable or not. It will decrease the amount of bounces and makes sure your domain doesn't get listed as spam.