Here is how to enable your alerts.

1. From the Mobile Email application, select the desired email account then press the center of the 5-way navigation pad to choose Select.
If prompted enter the username and password,  then press the center of the 5-way navigation pad to choose Sign In.
2. Press the right soft key to choose Options.
3. Select Settings then press the center of the 5-way navigation pad to choose Select.
 For AOL / AIM select Preferences.
4. Select the desired setting then press the right soft key to choose Save.

To disable the email alerts:

Select Disable or Never.

To enable email alerts:

Select Enable or Always.

To receive email during a desired time interval:

Select Only During then enter the desired time interval.
This setting may not be available on all handsets or accounts. Hope this helps