Frequency matters, and how often you send emails can have a significant impact on your revenue and email engagement (and unsubscribe) rates. Send too much and subscribers can suffer email fatigue causing them to disengage and unsubscribe. Send too few and you lose the attention of your audience. They may even forget why they signed up leading them to unsubscribe.
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).
Morgan, in Riding the Waves of Change (Jossey-Bass, 1988), suggests that one of the greatest limitations of the 4 Ps approach "is that it unconsciously emphasizes the inside–out view (looking from the company outwards), whereas the essence of marketing should be the outside–in approach". An inside-out approach is the traditional planning approach where the organisation identifies its desired goals and objectives which are often based around what has always been done. Marketing's task then becomes one of "selling" the organisation's products and messages to the "outside" or external stakeholders. In contrast, an outside-in approach first seeks to understand the needs and wants of the consumer.
A common example of permission marketing is a newsletter sent to an advertising firm's customers. Such newsletters inform customers of upcoming events or promotions, or new products. In this type of advertising, a company that wants to send a newsletter to their customers may ask them at the point of purchase if they would like to receive the newsletter.