Perform the following troubleshooting steps:
Check that your email settings are correct (consult with your email service provider). Go to the Home screen and select Accounts > your mailbox > Incoming email server and check settings. Also check the settings of the Outgoing email server.
Next troubleshoot your access point:
- Check the network quality on your device.
- Check that you are using the proper access point. You should use the access point that enables you to access websites using the Internet, don't use WAP.
- Try to connect to the email server by using different types of connections (3G - WLAN etc..) in order to guarantee a successful access to your email.
- Also check that other applications are working on the same Internet Access Point.
If the above does not help try the following steps:
- Remove the mailbox from your device.
- Restart your device.
- Try to define a new mailbox again.
- If that does not help, then reset your device to factory settings: On the Home screen select Settings > Reset phone. The lock code is needed, if you have protected your device by lock code. After reboot define your mailbox again.