E-mail tracking is used by individuals, e-mail marketers, spammers and phishers, to verify that e-mails are actually read by recipients, that email addresses are valid, and that the content of e-mails has made it past spam filters.
It can sometimes reveal if e-mails get forwarded (but not usually to whom). Some companies use it at the aggregate level to help determine the effectiveness of their sales and marketing messages. Other companies use it at the individual level to better understand a customer’s specific areas of interest. Many people use it to detect unauthorized forwarding and distribution of their copyrighted works and emails. When used effectively, it helps the company provide more timely, and more relevant information to the recipient. When used maliciously, it can be used to collect confidential information about businesses and individuals and to create more effective phishing schemes.
The tracking mechanisms employed are typically first-party cookies and web bugs.