I wonder why you're asking. What will you do with this info?

Each folder/subfolder is stored as a file in your filesystem. .sbd ("subdirectory") files record the structure, the hierarchy, so it knows which folders are subfolders of others.

mozmsgs files are digests of mailstore folders, provided in Windows to permit Windows search to interrogate the stored mail.

Yes, with POP-connected accounts, all of your messages are stored locally and there isn't any real difference between storing in an account or in Local Folders. One might choose to store messages together according to their context or subject matter, regardless of which actual email address they were initially sent to. Local Folders is an agnostic store, detached from actual email accounts. It's also significant for newsgroups, RSS feeds and the Outbox for sent messages pending a connection. And it's a sensible place for Saved Searĉh folders.

IMAP-connected accounts keep all their data on the server, but in Thunderbird you have local temporary copies held in the account folders. These are provided for your convenience, for faster searching, browsing etc. Since they track the contents of the associated server folder, messages in them will come and go as you download and delete messages. If you do want to keep something permanently, moving it to Local Folders is a practical way to make sure you have your own copy. Useful if you are parting company with an email account or its server and want to keep old messages that would otherwise disappear when the server becomes unavailable to you.

Everything is ultimately just a folder on your HDD, even if only temporarily in the case of IMAP-connected accounts.

Archives are for your convenience; they keep messages to hand where they can be browsed and searched, but not necessarily always in full view.

Some people (I'm thinking of my partner) simply don't "get" folders and organization. Everything would be jumbled together in one big folder. You appear to be the other extreme, perhaps over-thinking it.

Put your messages where it suits you and your own way of thinking and methodology. No method is particularly more efficient in terms of disk space usage, but may make a huge difference dependent on how you like to organize things. If you see no advantage to using Local Folders then ignore them. But be wary of Archives and other messages stored in IMAP accounts. You don't have full ownership of these.

Hi Zenos,

I keep trying to reply to you, but FF keeps freezing after a couple of lines in this thread. V odd, as I've been replying to Cor-el, in an FF thread OK. I've just tried a switch to OpenDNS, so, fingers crossed it may work this time!

It was good of you to explain the folders situation. My file system is a hang over from Outlook Express days, when I used to use separate dbxs for each subject, in order to keep them small to avoid corruption. In Tb, I've mostly stopped this detailed filing because the filtering and sorting facilities make it easier to leave a year's mail at a time in one folder.

I leave copies on server to make it easier to collect my historic mail when I change pc, or want another profile. This is fine, until there is a change at the isp end, as recently happened when virgin got their mail handling facilities back from Google. This resulted in me getting several thousand duplicates downloaded, when I turned on Tb the other day, after a long break.

I thought I had sussed the duplicates, by downloading the remove duplicates app, and getting my folders tidy again since I originally posted. However, this evening, I started to work, but there was a notice to compact all folders. Though in OE this was a very dangerous thing to allow, it has always worked smoothly in Tb. Unfortunately, this time, I noticed I had duplicates in my main inbox again, so I reran remove duplicates.

This seemed to have worked, but, when I started opening my mail, I found some messages were all text and code. Others had different message bodies to the headers, and very many have no message body at all.  :(

I'm not sure if the messages are corrupted before I open them, or some malware is erasing the contents as I open them; or if something is working its way through my mail boxes corrupting them in the background. Or if this was a one off compacting catastrophe. Or even if it was a bug in remove duplicates!

Nightmare scenario, as I've been too ill to be at the pc long enough to back everything up--and also, I wasn't sure, of the filing system, to know exactly what I was backing up: which was one of the reasons for my initial query.

I sure hope I can sort this, because I was using email as the 'database of my life', and there was loads of medical and gov dept, etc. correspondence on it!

Stupid of me to let it get to having to trust this, but I could not work out an easy way to make everything secure and bulletproof.  :(

Many thanks for your help.

At least it looks like FF hasn't crashed this time!

(y)

Just about sussed now.

Virgin had stopped showing a pop settings page, so I couldn't match Tb pop with virgin any more, and had to switch to IMAP.

They had put my gmail folder tree in a sub folder of 'my folders', so Tb had stopped seeing mail after Sept 29. It had continued adding to the sent folder though.

In various places, I now had sent items/inbox, and trash, under three different folder names, each, in three different file trees. On top of this, my phones had each created their own folders, and each was mapped to different ones, so I had to work out what was being sent where, and remap everything to the same boxes.

Very fiddly indeed, but I think I've managed to save most of the mail, and am still dealing with the backlog before rationalising all the boxes that aren't being used any more.

Apologies for not updating before now, but I've had a lot of trouble with Blur, as well, and couldn't get my log in details until now.

Cheers.