In a typical email marketing scenario, an organization builds an email list to reach or inform established and prospective customers. An email list may be complemented by a marketing database that allows for customization, data mining, precise targeting or other purposes. However, ubiquitous and unsolicited email, also known as spam, has made it difficult for ethical email marketers. Most email and Internet service providers (ISP) have significant filters to block spam, so getting legitimate messages across is easier said than done. Given this, email marketing has evolved into a specialized niche in digital marketing.