Thunderbird Archives and Local Folder Guidance Needed Please

Using Thunderbird v 68.0.1 on KDE desktop. I seek advice and guidance please.
I have three IMAP accounts set up on Thunderbird for different purposes or users and many thousand messages have accumulated on the server.
In order to make a start on reducing the server load my first effort has been to use the Archive facility within T’bird to move messages from the subscribed folders to the Archives folder keeping the existing structure in the account settings.
This seems to have worked well although subdirectories do not appear in the Archives folder until after I have closed T’bird and reopened the app but then all messages are where I had hoped.

My first question concerns the status of the messages once in the Archives folder. I believe the messages are still on the server and wish to understand the difference in status between messages in their normal subdirectory and those in the Archives subdirectory. For example can they be accessed by searches. I assume they take up the same space on the server although they could be compressed if wanted.

My second question concerns the Local Folders folder. If messages are stored in Local Folders, are they maintained also on the server although not active or are they removed from the server which might be expected and are they still saved within the T’bird profile on the local machine?

My third question is; once the messages have been moved into the Archives folder how may the whole Archives folder be moved to the Local Folders folder or somewhere outwith the profiles directory and put say on another machine for backup purposes. Should I leave the archived folders on the Local Folders and then back up everything remotely? I tried dragging and dropping to move the Archives folder to Local Folders but that didn’t work and there was no option in the right click menu. Hope this is clear.

My questions still apply except that I was able to drag and drop the Archives folder into a subdirectory in Local Folders. Took a while but I believe messages are all there now. Grateful for advice on moving the archives to backup machine. Should these files be left in T’bird format or converted to a more universal format I wonder?

Local folders means folders on your local machine, normally used with POP3. You can have Archive folders on the server or on the local machine. When you are using IMAP emails remain on the server for as long as you have configured them to remain on the server (your email provider may have to store them for a certain period to comply with local law). When you are using POP3 you can normally configure whether emails are deleted once downloaded or deleted after a set period (once again there may be local law regarding how soon your email provider can physically delete the emails as opposed to marking them as deleted).

The emails are stored in whatever format they were received by Thunderbird. You only need to convert them if you wish to export them to another email client without forwarding them to that email client.

Hi John,
Many thanks for your reply. As I stated at the outset I am using IMAP.

Do you have answers to my questions?
More specifically having dragged and dropped my Archives folder into a subfolder on the Local Folders it seems that the full set of Archives now exists in both folders so it appears there is a copy of the Archives folder in my Local Folders. What I need to be sure of now is if I can store the files from the Local Folders elsewhere and delete the Archives folder on my server and how may I reinstate these for retrieval if needed?

You should in theory be able to delete the emails in the Archives folders from the server - unless your email provider is implementing a local requirement to store emails for a certain time. You may or may not have permission to delete the actual folders.

I have never tried to restore folders to a server, only to a different local computer. So I cannot comment on that but you could create a Test folder on your local machine and see if Thunderbird is able to move it to the server.

Hi John,
Thanks for the suggestion. It is unfortunate that this subject is not well covered in the Thunderbird questions. There should be better information on the management of archived folders including storage and means for recovery. For example should archived messages be left in their native format or manipulated to make their access more universal should T’bird disappear. More important the implications for security, if any. For example how are archives to be accessed if the client account no longer exists?
What happens to attached files when messages are archived and how should one treat encrypted messages that have been archived. There is just not enough authoritative help regarding the recovery and use of archived messages but thanks for your contributions.