Many email marketers are offering free ebooks and newsletters as an opt-in bribe in return to email addresses. Though there is nothing wrong with offering such bribes, there are many other ways to grow your list massively.

Content library: For creating a premium content library, you don’t need to create the content from scratch. If you’ve already written and published epic blog posts, all you need to do is to repurpose them to a premium content library and encourage sign ups in order to access it.

Content upgrade: Unlike the usual opt-in giveaways, content upgrade provides exactly what a user need at the moment, because they are created specifically for each blog post. As the resource you offer is highly-targeted, it skyrockets the sign up rate.