When you delete or move files, then that email gets a 'marked as deleted' flag and is hidden from view. The email will appear in another folder, but the original 'marked as deleted' email is still taking up space in the original file. Compacting will remove it and tidy the file creating space. You may not be able to compact everything in one go, but you should be able to do it on individual folders, one at a time. Right click on folder and select 'Compact'. Suggest you start with the 'Junk' and 'Drafts' folders.

Emails are downloaded and if full copies are downloaded then they are stored in mbox (no extension) files, each email written to the file one after the other. So, it is more risky to have alot of emails in only a couple of files. I'm not sure how you organise emails, but it is recommended that you create folders and organise emails. This means you'll have smaller files, which makes it easier to perform compact. It is recommended that you keep the Inbox for incoming emails that need reading and organising and not for longer term storage.

If you have 'Attachments' in emails: You can choose to 'Detach' - them. This offers you the option of where to store those attachments eg: folder on desktop and in the email it will replace the attachment with a link. This means the size of email is reduced, but still offers a means of accessing any attachment in case you need to see it.

There is also the ability to choose to which folders can download full copies or just the headers. Downloading full copies uses a lot more space and is helpful if you need to create a backup of profile or use in Offline mode. You can also choose to only synchronise x number of days. Please note that regular compacting will be required to maintain it and remove emails older than the X number of days. These emails are only removed in Thunderbird and not on server. See info here under 'Disc Space Usage' and also 'Configuring synchronization and disk space usage'

• https://support.mozilla.org/en-US/kb/imap-synchronization#w_disk-space-usage

SAG167,

I can see why you would not have enough space to compact.

You post an interesting problem. And Toad-Hall has listed some possibilities, but I have some questions and additional thoughts.

> The first three IMAP files are 20.3GB, 17.7GB, 16.0GB.

1. Are the Inbox sizes?

2. When Thunderbird are bigger than the server, then compact is failing (because you don't have enough space, Antivirus is failing, or some other conflict) or there is a Thunderbird bug. So we need to ask a) what AV are you running, b) how much free disk space did you have?

3. Which of Toad-Halls items were helpful?

4. imap accounts are a good thing - that means we can just delete the files on your disk, and Thunderbird will re-sync the contents from the server, at the proper size.

If your problem hasn't been solved, please post an update.

(But even if it was solved, it would be nice to hear from you whether Toad-Hall's information was useful.)

Hi guys, yes, sorry, I have forgotten to follow up.

So I found out I had a major problem with my Mac. The time machine was stuck and for some reason, it kept making snapshots every time it found some space, but not cancelling the oldest. I have been in an evil loop for a while...

Then I had to format my Mac and start it again from scratch as it were brand new. So I eventually fix Thunderbird too.

Thanks, S.