This guide explains how to change the frequency that Thunderbird checks for new mail for each separate POP E-mail Account.
1. Right click on the Account you wish to change.
2. Choose Properties on the drop-down menu by clicking on it to get to Account Settings.
3. Click on Server Settings. Make sure “Check for new messages every XX minutes” is checked, and then enter the frequency in minutes in the box provided. Entering “15” will cause Thunderbird to check for new E-Mail on that account every 15 minutes.
4. Click on the “OK” button to save your setting.