In this scenario, a subscription check box is pre-selected for users to receive promotional emails where they would be including their email address (during a purchase process, for example). By leaving the checked box intact, users consent to receive email from you. This option is not flawless, as some users may not realize they’ve given their permission to receive marketing email and could be much more likely to report your email as spam, resulting in damage to your sending reputation and your company.
You can use this strategy to your advantage and increase your email list by giving people an incentive in return for their email. The giveaway could be free access to an e-book, a report, a gift hamper, or perhaps a lucky draw where people enter their emails and get a chance to win. A tantalizing offer is all you need for people to comply. For example: