Yes, IMAP accounts can be downloaded to the PC, and can later be moved to Local storage, and then deleted from the account. Keeping all downloaded is an option to set and you can also specify which folders.

After moving an account to Local Folders... Is there any way to delete contents of folders on the server but leave folder structure?

Reason for asking... I have 40 to 50 sub-folders... so after I backup the accounts emails to a "Local Folder" ... If I delete everything on the mail server for the email account... I would have to manually recreate all the sub-folders...

Thanks for any help.

You are actually going to suffer some pain if you continue to look at moving messages from an IMAP account to local folders as some sort of backup solution. This does work, but it has significant issues when the numbers of mails moved gets more than about 50. Sometimes less. They just disappear, or get duplicated. Depending on where the timeout occurs.

You should also be aware that you can not successfully copy whole folders of mail bu moving or copying the folder. The IMAP protocol just does not move folders. It can create them and delete them, but knows nothing of moving them or copying them. Let alone their contents.

To keep server storage under control you need to use a somewhat convoluted process to get all your mail into local folders.

Use the import export tools addon to export all the mail in the each folder to either an mbox file or an eml file. https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools-ng/?src=ss

This process can be slow as each local copy must be verified against the server copy and then exported. (this happen when you drag an individual mail as well) once you have the local, exported copies, you can import them back to local folders in Thunderbird and delete the server copies. (ctrl+A selects the entire contents of a folder). This process is a little messy, but 100% reliable. That can not be said for internal moves/copies when the numbers begin to push the bandwidth and connection speed.

Matt, I'm a little confused by your post.

Here is my Thunderbird setup: Tools > Account Settings > Server Settings with these options were checked... .. "Keep messages in all folders for this account on this computer" .. Synchronize all messages locally regardless of age .. Don't delete any messages .. Always keep starred messages

Question 1: To me this means that all email remains on the server and also is downloaded to my Win10 PC... right?

And, I have Thunderbird setup for 10-email accounts. - and for each of them I have dragged their respective folders to a corresponding folder under "Local Storage" - some of these email accounts have over 1000 to 2000 emails. - They all appear to have been "copied" correctly to their corresponding Local Folder

Question 2 - Are you telling me the above technique doesn't work reliably in Thunderbird?

Question 3 - Since I have the Thunderbird Server Settings setup to... - "Keep all messages in all folders for this account on this computer"" - Couldn't I just copy the Thunderbird Profile Folder(s) to another computer or external or cloud storage?

Maybe I misunderstood your response so please let me know if I need to resort to import/export to safely backup all my emails.

Thanks

Matt, I'm a little confused by your post. Here is my Thunderbird setup: Tools > Account Settings > Server Settings with these options were checked... .. "Keep messages in all folders for this account on this computer" .. Synchronize all messages locally regardless of age .. Don't delete any messages .. Always keep starred messages Question 1: To me this means that all email remains on the server and also is downloaded to my Win10 PC... right?

Sure. But it is only a sort of cache. Thunderbird will delete the entirety of it's store for the account if it can not contact the server. So hardly the archive most think it is.

And, I have Thunderbird setup for 10-email accounts. - and for each of them I have dragged their respective folders to a corresponding folder under "Local Storage" - some of these email accounts have over 1000 to 2000 emails. - They all appear to have been "copied" correctly to their corresponding Local Folder

I did not say it would not work, only that it was unreliable. But hey I am used to folk moving thousands or tens of thousands of mail in a folder. It is something which does not scale well.

Question 2 - Are you telling me the above technique doesn't work reliably in Thunderbird?

Yes

Question 3 - Since I have the Thunderbird Server Settings setup to... - "Keep all messages in all folders for this account on this computer"" - Couldn't I just copy the Thunderbird Profile Folder(s) to another computer or external or cloud storage?

That is the bit folk apparently miss, regardless of your local settings, in IMAP the server is the canonical authority and overrides your settings in Thunderbird.

Maybe I misunderstood your response so please let me know if I need to resort to import/export to safely backup all my emails. Thanks

I though I did that in my first response. The copying of mail to local folders from IMAP account is not reliable and errors in the process are basically not reported. The situation is improving, but it is not there yet. At least I would not risk business records on it.

Matt, thanks for the additional info. Regarding using the Export add-on... - Will it "export" all folders and subfolders for an email account... - or must you "export" each individual folder individually? Thanks again for your kind assistance.

As I do not export IMAP accounts, I can not really answer that question. However the menu it offers would indicate it does.

Personally I tend to use google mail accounts for high volume accounts and use their takeout service to make the mbox file I can import to Thunderbird. It takes them a couple of days to email a link to the export. But it sure takes a load off my local bandwidth and computer in generating them