Reduce the folder size of Thunderbird

I experienced some troubles installing files on my system and discovered that my partition with Windows was having only 50 megabytes of free space. This was astonishing because it is a 10 gigabyte partition with only Windows and some tools that occupy no more than 3 gigabytes. A quick check revealed that the mail folders from Thunderbird would occupy more than 3 gigabytes of space in the application data folder on the partition.

The folder size of my Inbox for instance with 100 mails was more than 500 megabytes which could not be true at all. I remembered that Thunderbird did not delete the mails even though they would have been deleted in the trash. This was the cause for the discrepancy between the meager amount of mails and their size and the big huge mail folders on my c: partition.

The solution nevertheless is pretty easy. All that needs to be done is compact the folders which removes all deleted mails immediately. I was able to reduce the folder size of my Thunderbird folders from more than 3 gigabytes to 300.000 kilobytes freeing up valuable disk space on my main partition.

Just right-click a folder and select compact this folder to remove all deleted emails and keep only emails that are visible in Thunderbird. You could check the Disk Space option to automatically compact folders if that saves a defined amount of kilobytes. (You find the option under the advanced tab and offline & disk space tab in the Thunderbird options).