Right click the folder and select Compact to do individual folders. Most of the horror stories are from people that do not Compact on a regular basis. Compacting is a needed maintenance task and it needs to be done frequently.

Thanks, but a further question.

Exactly what happens if I do allow the system to compact my folders (and clear up the now 3.9 GB of space)? Will it ONLY remove previously deleted emails, or also emails I want to keep? And no, I do not regularly compact -- thus my quandary. I do not compact, period. I've been afraid to lose vital emails.

I hope you do backups since your neglect of proper folder maintenance will guarantee a failure sooner than later. In Thunderbird when you delete a message it is marked for deletion and hidden. Compacting removes those marked for deletion files. Lack of regular maintenance causes file corruption and then compaction does unpredictable things including removing too many messages. Despite the poorly chosen name, compacting has nothing to do with compressing or zipping files. The way it saves space is removing marked for deletion files. It works great when done regularly.

1) I back my system with Carbonite.

2) So compacting will remove ONLY deleted files?

3) How do I make sure I don't lose any of the emails I do NOT want deleted?

Thanks.

re: 1) I back my system with Carbonite.

If you use an IMAP mail account then make sure the subscribed folders have been synchronised to get a copy into your thunderbird profile else you will discover you have only backed up a load of headers. I would also advise you exit Thunderbird before backing up Profile.

Make sure you have backed up the actual Profile folder. Info located here:

• http://kb.mozillazine.org/Profile_folder_-_Thunderbird
• http://kb.mozillazine.org/Profile_backup

Personally, I usually just do a simple manual copy paste of the Profile folder to an external drive as it takes a matter of seconds to do.

re :2) So compacting will remove ONLY deleted files? Compacting only removes 'marked as deleted' emails. Compacting a corrupted file can cause loss of good emails.

Background info: Emails are stored in mbox files. They are written one after the other in the file. So that file document gets longer and longer as emails are added. When you delete an email, it becomes 'marked as deleted' but remains in the file. So you can imagine one long document with each email like a paragraph. Then think of various 'paragraphs' that need editing/removal by compacting. So, compacting frequently on the Inbox and Junk (which usually get more activity than otjher folders) will help to maintain a healthy file.

re: 3) How do I make sure I don't lose any of the emails I do NOT want deleted?

If you want to compact only eg: Inbox and you have not been maintaining that folder by regular compacting and you are unsure if there is any corruption in that folder, do this as a precauction:

• Move all good emails into another folder.
• Delete anything you do not want.
• Empty deleted folder.
• Right click on Inbox folder and select: Compact

Recommend: It is best to keep the Inbox as a working Inbox for incoming mail and not as general store. Good advise here:

• http://kb.mozillazine.org/Keep_it_working_%28Thunderbird%29

I'm going through individual folders and compacting individual modules (drafts, trash, sent).

It seems to be working so far. The 3.9 GB to save got down to 2.5 (then back to 2.6)

Thanks.

To explain how compact works is difficult, but the principal is simple.

Thunderbird maintains an index it uses to populate your lists of mails. This index has an offset into the underlying mbox file. for the location and size of the related email.

You select compact and Thunderbird uses that index working from oldest to newest, getting the mail that is displayed and writing it to a new file. Once the process is completed the old store is deleted and the new file is renamed to replace the old file. Then the new file is used to regenerate the index. (the same as right click and selecting repair)

Most horror stories have nothing to do with that process. They actually relate to the process identifying that at some point the whole mail store has been removed. The index is stale so the compact end with apparent dataloss.

True there was data loss, but not at the point of compact. There are numerous reasons why this can occur. But by far the most common is anti virus programs deleting the entire mail file to remove a very minor threat and being proud of their detection and automatic removal. They do not delete the index (which is a shame as the data loss would be obvious immediately)

I have had long discussion with some of the developers. They maintain that they can do very little more to guard against this sort of issue as it usually occurs when Thunderbird is not running at all.

The short is, do not believe everything you see about Compacting. It certainly highlights data-loss. But is very rarely the actual cause.

Thanks to all.

I've compacted every individual folder I have, and went to set up automatic compacting.

Doing so, I've now found that my computer was ALREADY set to automatically compact at 20 MB. I learned how to do something, but don't get why the system didn't do what it was already set to do.