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.
From a model-building perspective, the 4 Ps has attracted a number of criticisms. Well-designed models should exhibit clearly defined categories that are mutually exclusive, with no overlap. Yet, the 4 Ps model has extensive overlapping problems. Some of the Ps are only defined in vague terms. Several authors stress the hybrid nature of the fourth P, mentioning the presence of two important dimensions, "communication" (general and informative communications such as public relations and corporate communications) and "promotion" (persuasive communications such as advertising and direct selling). Certain marketing activities, such as personal selling, may be classified as either promotion or as part of the place (i.e. distribution) element.[47] Some pricing tactics such as promotional pricing can be classified as price variables or promotional variables and therefore also exhibit some overlap.
Needs: Something necessary for people to live a healthy, stable and safe life. When needs remain unfulfilled, there is a clear adverse outcome: a dysfunction or death. Needs can be objective and physical, such as the need for food, water, and shelter; or subjective and psychological, such as the need to belong to a family or social group and the need for self-esteem. 																		

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.[12] 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.