"Thunderbird" is an open-source e-mail client developed by Mozilla. By default "Thunderbird" stores all e-mails, contacts, and settings in separate folders within the "Profile" folder. The maximum size of each folder in this directory is 4 GB. However, you can increase your mailbox limit by storing the "Mail" folder on any drive or directory located outside of the "Profile" folder. This means your mailbox limit is determined by how much free disk space you have on your computer. Moving the "Mail" folder outside of the "Profile" folder is a quick and simple process.
Click the "Start" button on the task bar and press "Computer." Select the location where you would like to store your mail.
Press the "New folder" button in the toolbar and provide a name for the new folder.
Click on your personal folder in the left-hand navigation pane.
Double-click "AppData" and open the "Roaming" folder. Select "Thunderbird" from the list of applications and open the "Profiles" folder.
Double-click on your profile folder and highlight the "Mail" folder. Click the "Organize" button in the toolbar and select "Copy" from the drop-down menu.
Navigate to the new folder. Click the "Organize" button in the toolbar and select "Paste" from the drop-down menu.
Open "Thunderbird." Click "Tools" in the menu bar and navigate to "Account Settings."
Click on your account name and press "Server Settings." Click the "Browse" button and highlight the new folder in the dialogue box. Press "OK" to confirm.
Restart "Thunderbird" to put the changes into effect.
Only delete the "Mail" folder from your profile folder once you are certain that "Thunderbird" recognises the new save location.