Hi KaTo, I'm going to flag your question to move from Firefox to Thunderbird.

Meanwhile, according to a web search, a .sbd file is a subdirectory (mail folder) file, so please don't delete it until a Thunderbird expert can weigh in on options.

Copy mail from the gmail IMAP folders to subfolders of Local Folders, confirm the copy has succeeded, delete the messages from the IMAP folders, then compact them from the right-click menu. That will free up space on the IMAP server, and to backup the Local Folders to an external drive or other media, Help/Troubleshooting, Profile Folder, Open Folder, close TB, copy Mail/Local Folders to the backup location. The same could be done with the entire profile folder.

Hi shhowes,

Thank you for your quick response. Should these actions also free more space on my OS (C:)? It is now almost full although I have installed only one program/app which takes more than 5 GB. KaTo

Compacting all folders will remove messages that were deleted and made invisible, although still taking up space. You might find that that frees up sufficient storage, but if not I recommend you get an external drive or even a $20 128GB USB drive.

At the moment, my Gmail server's size is only 0.67 GB: Inbox has 27 messages, Sent has 130 messages, Social & Bin & Drafts have no messages. How it possible that my Roaming/Thunderbird/.../[Gmail].sbd still takes 143 GB. This does not make sense and is ridiculous.

Is there any easier way to solve the problem? If I disconnect my Gmail from my Thunderbird, would it solve the problem easier?

Did you compact all folders? Look through the account folder, ImapMail/imap.gmail.com in the profile folder, and find which mbox files - large files with no extension, named after folders - are the largest. Is All Mail a subscribed folder? It contains all gmail messages, and is usually not subscribed as it is redundant.

I am not very knowledgeable about the inner structure of computers, but I have compacted nothing. Please find attached the captures of the ImapMail/imap.gmail.com and ImapMail/imap.gmail.com/[Gmail].sbd. The images show the size of each folder. According to Properties, the size of ImapMail is 143 GB, and the size of [Gmail].sbd is the same. However, according to Gmail's server, its size is only 0.6 GB of 15 GB.

I thought, I already responded to your message above but when I came back here, I noticed that I could not see my previous message here.

My knowledge of the inner structure of computers is very limited. However, I have not compacted my folders. According to my Gmail service, my emails take 0.67 GB after cleaning it, but AppData/Roaming/Thunderbird/..../ImapMail/imap.gmailc.com says the size of this folder is 143 GB. How is this possible? I have never sent so many emails.

Please find attached the image of the structure of imap.gmail.com and the sizes of the folders under it, and the image of [Gmail].sbd and the sizes of the files under it.

My OS's size is about 240 GB, but it is almost full. The Apps and Features take about 189 GB although I do not have many apps there. The hidden files under AppData/Roaming/Thunderbird explain why it is almost full.

Do you know what I could do to solve this problem?

Unsubscribe from All Mail (right-click the account in the Folder Pane, Subscribe, uncheck All Mail), uncheck All Mail in Account Settings, Synchronization & Storage, Advanced, open the profile folder, close TB, delete All Mail and All Mail.msf from the local directory. That will free up about 150 GB. Restart TB, select File/Compact Folders.

See the All Mail section here.

Hi Sfhowes, Thank you so much for solving the problem. Now my computer has 151 GB of free space! One final question: I was able to take all the other steps you mentioned above, but I do not know what is the path to "select File/Compact Folders." What do you mean by this? Sorry that I am not very good at these kinds of things. KaTo

re :One final question: I was able to take all the other steps you mentioned above, but I do not know what is the path to "select File/Compact Folders." What do you mean by this?

Right click on a folder in the Folder Pane to see a drop down menu and then select 'Compact'.

A bit of helpful info: When you delete or move a message, that email is either moved to a folder of choice or if deleted goes to the Trash. In reality, the original email is still in the original folder, but it is now 'marked as deleted' and hidden from view. It is also taking up space and making that folder appear much larger than you might have expected. When you compact the folder, all those 'marked as deleted' emails are properly removed. This makes the file mbox file that contains emails tidy, frees up space and means the file is less prone to becoming corrupt. It is basic good housekeeping on the file. https://support.mozilla.org/en-US/kb/compacting-folders

The problem is that I do not know where I can find the File/Compact Folders. Are you talking about AppData/Roaming....../[Gmail].sbd? If I right-click there, I cannot see a Compact option. I cannot also find this from TB or anywhere else. Please send me detailed instructions how to find the right place. Thanks

Compact Folders is on the File menu. On Windows, the menu bar is hidden by default but may be displayed if you tap the Alt key or F10 key. Does that work on yours?

Open TB and press Alt if the Menu Bar with File is hidden. File/Compact Folders is also under the 3-bar menu icon at the upper right corner.

Thank you. It was not visible under the 3-bar menu icon at the upper right corner, but when I pressed Alt, the menu appeared. Great!

re : It was not visible under the 3-bar menu icon Image as guide: