Internet Access
To check your email account from a Nintendo DSi device, you must have access and be currently connected to wireless Internet network. You can either connect to a public Wi-Fi network, which is open to everyone and does not require a key, or a secured network to which you have the required network key. The DSi cannot connect to a wired Internet network.
Getting Internet
Your Nintendo DSi is not connected to wireless Internet by default. To get connected to the Internet, power on the device and click the green "Start" icon with a wrench. After going to the third page of the system settings menu, choose "Internet" from the list of options. Choose "Connection Settings" and then the "None" button next to "Connection 1." When you choose "Search for an Access Point," your DSi will display the nearest wireless networks -- click on one to select it for connection.
Checking Email
To check email, you must have a Web browser game downloaded to your device, such as the Nintendo DSi Browser, available in the game shop. Once the browser is open, click the "Go to Page" button and enter the URL for your email provider's homepage. For instance, if you use Hotmail, point the browser to hotmail.com. Enter your username and password like you normally would on a computer to gain access to your account.
Privacy Consideration
Just as with any computer, using a secured wireless network provides a higher level of security. If you elect to use a public wireless network on your DSi, be aware that it will be easier for someone to intercept the information you exchange -- including incoming and outgoing emails.