Are you subscribed to the All Mail folder? It usually takes a lot of space, and most users can unsubscribe and delete the mbox file. See the All Mail section here.

Define which folders are allowed to download and store message bodies and which ones download headers only in the Message Synchronizing section of Synchronization & Storage in Tools/Account Settings. If you switch from full bodies to headers only, the mbox file for the folder can be deleted as with All Mail, or backed up to an external location. As always, compacting folders will free up space used by deleted messages that are hidden but not removed from the computer.

> I want to keep the headers so I can download them from the server later at my leisure. Is there any way to do this?

Not unless you are using pop. And iirc, google is discontinuing pop in the not too distant future?

[Addition: you can download only imap headers by disabling syncing of message bodies, but only on a per account basis, not per message]

> Are you subscribed to the All Mail folder? It usually takes a lot of space, and most users can unsubscribe and delete the mbox file. See the All Mail section here.

Under normal circumstances the gmail "All Mail" folder should incur a performance penalty, not a disk space penalty. The space issue was resolved in the time frame of version 18, perhaps Bug 721316 - Use Gmail IMAP Extension of X-GM-MSGID, X-GM-THRID, X-GM-LABELS in addition to XLIST (I'm not 100% certain this is the correct bug report but it's in that area)

I don't seem to be using POP. Everything I look at references IMAP.

I am not subscribed to AllMail. I turned that off a long time ago for disk space reasons. I didn't know until now that there was no disk space penalty.

If I were to shutdown Thunderbird and move some of the larger account sub-folders to an external hard drive, would that adversely affect Thunderbird? Or would it just recreate the folder with nothing in it? Also would doing this affect GMail? I think auto-sync is off for Thunderbird at present since I have no new messages and every time I click on an account sub-folder, Thunderbird wants to log in to GMail. Since I have to explicitly let it access GMail, I don't think there is any syncing going on. Is there any other way to verify auto-sync is off?

Thank you MistWing SilverTail

> Under normal circumstances the gmail "All Mail" folder should incur a performance penalty, not a disk space penalty. The space issue was resolved in the time frame of version 18, perhaps Bug 721316 - Use Gmail IMAP Extension of X-GM-MSGID, X-GM-THRID, X-GM-LABELS in addition to XLIST (I'm not 100% certain this is the correct bug report but it's in that area)

Not sure that there's no space penalty, since if subscribed folders are set for offline access, there will be mbox files for every subscribed folder, including All Mail if it's subscribed. Unsubscribing All Mail and deleting its mbox and msf files, as explained in the kb article, will definitely free up space.

I don't seem to be using POP. Everything I look at references IMAP. I am not subscribed to AllMail. I turned that off a long time ago for disk space reasons. I didn't know until now that there was no disk space penalty. If I were to shutdown Thunderbird and move some of the larger account sub-folders to an external hard drive, would that adversely affect Thunderbird? Or would it just recreate the folder with nothing in it? Also would doing this affect GMail? I think auto-sync is off for Thunderbird at present since I have no new messages and every time I click on an account sub-folder, Thunderbird wants to log in to GMail. Since I have to explicitly let it access GMail, I don't think there is any syncing going on. Is there any other way to verify auto-sync is off? Thank you MistWing SilverTail

Export the folders from TB with e.g. ImportExportTools NG, to an external location, then unsubscribe the folder (or set it to headers only), and delete the mbox and msf files (or keep it subscribed, headers only, delete the mbox).

I think you can only disable auto-sync by going File/Offline/Work Offline, otherwise every time you open a folder it will sync with the server.

Correct, certainly there will be an mbox for every folder, including the All Mail folder. The cited bug does not eliminate that requirement. But that doesn't mean that "All Mail" contains the body of every message.

Note the KB says "... only ONE copy of every newly downloaded message is kept on disk, so there is no need to unsubcribe from a storage point of view.)". The reason for that fixed bug is to avoid message body duplication - only one folder in a gmail account should contain the message body, but the message can be referenced in multiple folders.

Thus, it is possible in the case of a gmail account for the folder to only have the message header. This is an exception to what I previously stated, about message sync not capable of avoiding local message bodies on a per message basis.

I understand the principle of not duplicating message bodies, but I know from my own experience that the All Mail mbox can be much larger than it would be if it just contained headers, and a recent user eliminated over 100GB by deleting the All Mail mbox.

If Autosync is off, then the clean approach to recovering disk space is just close Thunderbird and delete the .msf and mbox (no file extension) for each folder.

But you haven't said how much space is being used on disk, and whether that is in excess of what your server indicates.

> If I were to shutdown Thunderbird and move some of the larger account sub-folders to an external hard drive, would that adversely affect Thunderbird?

How would you reference this information?

I understand the principle of not duplicating message bodies, but I know from my own experience that the All Mail mbox can be much larger than it would be if it just contained headers, and a recent user eliminated over 100GB by deleting the All Mail mbox.

Was it reported as a bug? If not, it should be.

Regarding the space, the folders on my computer total 112 GB, the emails on GMail are using 96 GB out of 201 GB available. The lack on syncing is likely the reason for the discrepancy.

Accessing the information is something that would be done later when I have gotten more space back on my computer. According to things I've read, I would be able to copy the files back to the appropriate folders for Thunderbird to read them. I've done this with the e-mails in the 'Local Folders'. I'm thinking that I can load the saved files there. I have a small folder with e-mails that aren't important and I can use that to test this. I just wanted to know if this was something that was already known to work or not work.

Thanks MistWing SilverTail

Yes, if you save or export a folder as an mbox file or eml files, they can always be imported to Local Folders. The mbox file is copied into the Mail/Local Folders location of the profile folder, while TB is closed, and eml files can be dragged from File Explorer and dropped onto a subfolder of Local Folders in the Folder Pane (while TB is open).