The Definition of an Opt-In Email List [In Under 100 Words]

An opt-in email list is a list of email contacts that you've acquired because they've voluntarily given you their contact information.

Although it may seem easier to purchase or rent email lists, that can have serious consequences on your email marketing success -- particularly your ability to get delivered into people's inboxes.

Not only do purchased or rented contacts not want to hear from you, but reputable ESPs won't let you send emails to contacts that aren't opt-in.

To learn how to grow an opt-in email list full of contacts that actually requested to hear from you, read this post.