Hi, I read your question and have a question. For the 58.4GB account, where do you get those sizes 58.4GB and 18.9GB?

The larger value is what I get when I right click the folder in which my email is stored in Windows Explorer. The smaller value is what is listed in Thunderbird when I set the view to show the folder sizes in the left pane.

Incidentally, I manage the IMAP store, and the smaller values match the space consumed on the server folders as well. It appears that Thunderbird is possibly duplicating things in the mbox files that it istoring on my local system.

Are you using version 60?

Yes, 60.2.1

Did you enable the windows search option when you installed Thunderbird? That creates duplicates of mails (limited to 40Kb per mail). In my case it was over 100,000 of them that I had to manually remove after I disabled the setting in options.

I don't think I did, but I'm not sure. Is there a way I can check and turn it off now?

Just found the setting. No, Windows search was not and is not enabled in my installation.

re :The larger value is what I get when I right click the folder in which my email is stored in Windows Explorer.

Could you post an image of this and tell us which 'folder' you are talking about. I need to know this because emails are stored in files not folders, so you may be looking at a folder that contains a lot more than first imagined.

re :The smaller value is what is listed in Thunderbird when I set the view to show the folder sizes in the left pane.

Post image of Folder Pane showing sizes.

I deleted the store of emails on my local hard drive right after my initial post, and that store has not yet bloated up again the way it was when I first made the post, so I don't have anything to show in a screenshot. I'm aware of how the emails are stored on the hard drive (single mbox file per folder within the IMAP structure). However, the size that Thunderbird reports for any given IMAP folder is smaller than the mbox file when this bloating occurs.

I'll put up an image when the folders bloat up again, but there is certainly something wrong when the hard drive is storing three times the size reported in Thunderbird.

OK, the folders blew up again, so I have images of the following: 1) The folder pane on the left side of Thunderbird with the size column showing. 2) A screenshot of the properties window for the folder where my emails are stored on the local hard drive.

You can see here that Thunderbird indicates the entire DSI shared account should be 19082MB. However, on the hard drive, it is 32.5 GB.

To show a more specific example, the following two pictures show that the highlighted folder in Thunderbird should be 16MB, but the corresponding MSF file on my local hard drive is 33.1MB.

So, somehow, the individual MSF files are duplicating information (I think). Any ideas why this may be happening?

Who is the email provider - gmail?

No, it's a self-hosted IMAP on a Synology NAS.

I have something interesting to add. As I said, I often run multiXpunge to ensure my folders are all compacted. As I was doing it earlier today, I noticed that the status in the bottom left corner indicated that the account was "downloading message header Y of X" where Y was much larger than X. I include a screenshot here. Is this possibly an indication of what's going on here?

I think some diagnostics on the server software might be in order. What IMAP server are you running?

It's just the standard MailServer application on the Synology DSM

Email is stored with uuencoded images. This greatly enlarges the storage size. Perhaps Thunderbird is reporting the size if images are saved out as GIF or JPG, not the uuencoded size.

Is the way it's stored on the IMAP server any different than how it's stored in my local hard drive (in terms of how images would affect it)? When Thunderbird initially downloads the emails in the account, the total folder size closely matches what Thunderbird reports, and also closely matches the size of the folder on the IMAP server. It's only after some time that the local folder size seems to blow up.

I haven't confirmed that there's a link, but I think that the last time the folder size blew up was after I searched the folders for an email. Might indexing the emails be adding a huge amount of data to the email files?

Thunderbird reports the full message size, which is the same as the server size, which is the encoded form where appropriate. Indexing size is not included.

I have some more information on this issue. As I have multiple computers working with the same IMAP accounts, I have been waiting to see if one will "inflate" the files while the other remains "uninflated". My laptop inflated yesterday so I found a email store file to compare from each system.

The IMAP folder contains one email. When I open the corresponding files, the uninflated one looks correct. The inflated one, on the other hand, has the entire email repeated four times within the file. The only difference I notice from one of the repeats to the next is the date following the "From" line at the very top of each.

It looks like Thunderbird is just downloading the same email over and over and saving repeat copies into the file connected to the IMAP folder.

Anyone have any ideas? Thanks!