Why should you clean your email lists with something like Email Hippo?
As an email marketer, you very well may be buying or scraping leads to send cold email campaigns to. And while some people have the knee jerk reaction to call you a spammer, it's legal and common practice to send out cold email marketing, if you do it right.
In order to do it right, you should try to verify all the email addresses before you send campaigns to them. Email addresses go stale with time, as people leave their positions at companies, so your list could have bad email addresses in it.
It's important to clean up these lists regularly to get any bad email addresses off them to improve your deliverability and keep your email server's reputation clean so you can land in more inboxes and see more results.