To increase the amount of history kept in the Blackberry:

1. Open mail folder on blackberry
2. Press blackberry button and select “Options” from menu
3. Select “General Options”
4. Scroll to bottom of list and select “Keep Messages”
5. You will then be able to select keeping messages for: 15 days, 30 days, 2, 3, 4, 5, 6 months or forever
6. Save changes