It can directly boost revenue very quickly, making the impact of e-mail disproportionate to its low cost. In fact, in 2005 e-mail returned $57.25 for every dollar spent on it, according to the Direct Market Association's Power of Direct Marketing study released in October 2006.

Mass Emailing Benefits
Repeat purchases: cross-sell and up sell suggestions based on purchase activity into purchase
shipment Confirmation: inform customers of related products and new arrivals from the same lines as previously purchased items.
first-time purchase: Send an alert about new products in the same categories as recently browsed or searched items
Educate customers about recently browsed/searched products, especially those that may require a longer decision-making process; send user ratings or product reviews; include a compelling offer/incentive to buy now.
customer retention increase. Segmentation of e-mail responders and non responders targeting appropriate content and updates to each group to encourage the behavior we want.
Follow-up mails that reinforce the benefits the visitors will receive from the purchase; include a discount and/or another incentive, reminders of the limited time to take advantage of the offer etc.,

Email Addresses:
Most companies today have e-mail addresses for fewer than 20% of their customers. With the cost of acquiring a customer so high, it makes sense to expand the number of channels through which a customer can do business with you. This is simple to do; all you have to do is ask. At the transactional point, at the service counter, in the contact center, at the bottom of your media ads, invite customers to sign up for your e-mail list with a promise that you'll cherish their address and treat it with great respect.

By directing the offline channels to ask customers as part of almost every interaction to join the e-mail program. In this way, you will continually build an e-mail list of people who do business with you, like you, and want to learn about other offers relevant to them.