Examples: Gmail, Hotmail, yahoo, and many others.
ISP email is the e-mail address that you subscribe to when you are using the internet services of a particular provider. However, your e-mail address and inbox space cannot be used by you once you change you ISP.
When you change the ISP, you can no longer use the email address. In this way you lose your e-mails and telling all the people about a change in your address may be difficult.