I do have a bullet selecting "sync all messages locally regardless of age" (the other two options are not selected)

The section below this one about saving up disk space has a bullet on "not deleting any message" (and a tick on preserving starred messages)

sorry, I forgot to say that "' keep messages for this account on computer" is NOT selected for any of my two IMAP accounts

But is this selected:

'Keep messages for this account on this computer'

OR did you not select that option , but instead clicked on 'Advanced' and selected specific folders ? If you selected specific folders, is the folder you are having problems with actually selected?

I'm trying to understand your setup.

"keep is messages for this account on this computers" is NOT selected

Also, on "advanced settings" (below "keep messages for...") one of my imap accounts actually has several ticked folders (I don't think I voluntarily wanted to mark them for local management), while the other account does not have any folder with a tick. Both accounts have a problem when compacting, anyway.

re :Also, on "advanced settings" (below "keep messages for...") one of my imap accounts actually has several ticked folders

For that particular imap mail account in the Account Setttings > Synchronization & Storage Can you make sure that only the folders you see in your Folder Pane are shown as selected to synchronise in the 'Advanced' section. click on OK

Then check the Offline settings here;

Tools > Options > Advanced > 'Network & Disk Space' tab click on 'Offline' button

At the bottom where it says: 'Download messages for offline use when going offline' Select either 'Yes' (or 'Ask me') click on OK Click on OK

'File' > 'Offline' > 'Work Offline' you may get a prompt if you set 'Ask me', but select yes to download and synch to work offline.

Allow time for download to occur. Then try 'File' > 'Compact folders'.

Please report back on results.

Thank you, Toad-Hall,

I followed your steps.

Some main folders on the "sync and storage" menu were actually not ticked, so I ticked them, as they were visible on my Folder pane on TB main window.

After a long and massive message download, I compacted and.... same error occurs, again.

Now if I restart TB the e-mail account appears on online mode (same error occurs if I try to compact) and if I set it to "work offline", compacting is greyed.

I'm (really) worried that this process has meant that TB is now using a lot more of space in my HDD. Is that correct? if yes, is this process reversible?

Yes... now my roaming folder (windows) occupies more than 1.5 GB (before only 250 MB).

Please, any solution to this new problem?

As hard drive space is an issue for you. You could use the option to only download the last eg: thirty days. Over time this will increase what is stored, but it will not download and store old emails, so releasing space. All emails are still accessible and stored on the server.

'Tools' > 'Account Settings' > 'Synchronization & storeage' for the imap mail account that has loads of emails stored in Thunderbird. Under 'disk space' section select 'synchronize the most recent eg: '30' days'

You also choose not to store locally any particular folders. 'click on 'Advanced' button to see list. uncheck anything you do not want to download and store as copies in Thunderbird.

click on OK

Then, whilst you have a load of emails currently stored in Thunderbird, I would take the opportunity to create a backup before doing anything.

You can manually backup your profile folder name which is usually called 'xxxxxxxxx.default' where the x's are letters and numbers.

In Thunderbird

• Help > Troubleshooting Information
• Click on 'show folder' button

a new window opens showing the 'contents' of the 'profile folder name'.

• Close thunderbird now - this is important.

• Go up the directory and Copy/paste the 'profile folder name' folder to an external drive/storage device.

When you have done this to create a backup, proceed with the following.

• Then reselect the profile folder name to see contents.
• click on 'ImapMail' folder
• click on the imap mail account folder which has loads of emails stored.
• Delete all files and folders in the imap mail account folder, so leaving an empty imap mail account folder.

• Restart Thunderbird.

As emails are stored on server, you should get all files and folders back. This time it should download and store in Thunderbird only the selected folders and also the last eg: 30 days worth of emails (assuming you chose this option).

Sorry, I'm late (I received no notifications of your answer).

I did what you said and now TB default user occupies far less.

The original problem with compacting persists (even for clean installations in a different computer)... but, I am now a little bored of that problem, so let's wait for better times.

Thanks