Online gambling providers require customers to allow email messages from the provider. This requirement provides gambling marketers an inexpensive and potent medium to encourage frequent gambling, higher bets, and other potentially harmful behaviors that may lead to problem gambling. An online casino was developed in 2000 to collect data on online gamblers' actual gambling behavior after receiving persuasive permission email messages. Data were collected over a 36 day period. One of five permission email messages in an online gambling experiment had a significant and large effect in increasing expected gambler retention by an average 20 days. Increasing the length of play is a primary objective of gambling venue owners who often use CRM programs and permission email marketing to increase revenues. This finding adds knowledge to the possible promotional strategies that extends a gambler's lifetime value with an online betting company, offering a competitive advantage to gambling website operators.