The huge advantage of email over social media is that prospects and customers are more likely to see an email than social media. Just posting something doesn't mean that everyone you want to see your message will see it. Your post might not even show up in your targets' social media streams. However, an email will sit in the inbox until it's read (or deleted).
While almost all reputable email service providers work very hard to make sure that your emails are not blocked by major ISP’s, they can’t control whether or not your emails hit the inbox or the spam box. Although most will help you by providing a quality score to help you determine availability, getting whitelisted is the most effective way to ensure that your emails get delivered properly.