Compacting folders

How to compact folders

It is a good idea to periodically compact your mail folders in Thunderbird. To do this, simply click on one of your accounts (or a folder in the account) in the folders pane, and then go to the File menu and select Compact Folders. It is also possible to compact a single mail folder by right-clicking on that folder and selecting Compact This Folder. If you are using Thunderbird with offline support, you can go to File > Offline > Offline Settings, and check the "Compact folders when it will save over ___ KB."

What it does

When you delete a message, that message does not actually get removed from the mail file. It is simply marked as deleted and becomes invisible from within the application. When you empty the Trash folder, the messages stored there are marked as deleted and made invisible, but they still in fact exist in mail file named Trash. It is only when you compact folders that the "deleted" messages are really erased from the mail file.

What if you don't compact folders?

If you rarely or never compact folders, your mail files will accumulate more and more messages that have been marked as deleted but have not been truly erased. This can have negative effects with regard to disk space and Thunderbird performance:

• Even if a mail folder seems to be empty or nearly empty, the mail file can become dozen or even hundreds of MB in size. [1][2][3] This will use up disk space that could otherwise be free, and when you make backups of your mail files for safekeeping, you'll be backing up all these "deleted" messages as well.

• Messages that you have deleted or moved to other folders can strangely reappear where they shouldn't be. [4][5]

• It could cause problems when you try to defrag your hard disk. [6]