The answer is quite simple - Email is the ¹1 application on the Internet. Email helps increase the stickiness of your site by giving users a reason to return and visit often. People are signing up for new email addresses everyday and desire a domain that is easy to remember and reflects their personal/business interests.
There are numerous free email providers out there and the tricky part is finding what you are looking for in an email application. The list below outlines some things to keep in mind when you are choosing an email application for your site.
1. Privacy - Is the email service web-based and password-protected?
2. Global Accessibility – Can you send and receive email from any computer with any browser from anywhere in the world?
3. Permanency – Will your account and email address be active forever?
4. Spam Issues – Can the email service block spam before it reaches your inbox?
5. Personalization - Can you choose your own personalized email address?
6. Versatility – Are there attachment capabilities so you can send images, photos, or documents?
7. Attachment Size – Is there a limited or unlimited attachment size?
8. Storage – How much storage does the email service provide per box?
9. Filters – Are there filters that can be customized to allow you to control incoming mail?
10. Address Book – Does the email service include an easy-to-use address book?
11. HTML Mail – Does the email service offer HTML capabilities?
12. Personal Signature – Can you create and personalize a signature to be included at the end of each email message you send?
13. POP Mail Retrieval – Can you retrieve messages from your POP email accounts, such as work or school?
14. Message Search – Can you search the message body, header, or folders for messages containing particular words or phrases?
15. Built-In Help – Can you get help instantly?
16. Cost – Is the email service free or is there a cost involved?
Another great benefit to consider is the ability to offer your visitors email addresses @YourDomain. The Email service can be branded to your site specifically so your domain name has a presence on every email message sent. One such email provider that offers a branded email application for no cost is Everyone.net. This service also allows the site owner to generate income through significant advertising and subscription revenues. More information can be found at www.everyonemail.net.
In summary, by offering your users an email service through your site you are giving them one more reason to regularly return. Increase your site traffic and user return visits, increase user time spent on your pages, and potentially increase your revenue stream – all by adding a simple, fully integrated email application to your site.

