It is best to keep 'Local Folders' name as 'Local Folders' as 'Archive' is used as a special name folder not an account name. It is also less confusing. 'Local Folders' mail account refers to an account with emails stored locally on your computer.

Then create an 'Archives' folder in 'Local Folders' mail account.

Usually, accounts are set up to contain their own 'Archives' folder, so emails are still stored on server but are no longer occupying the more regulary used folders. So it has a decluttering effect and helps to keep files small providing the 'Archives' folder contains subfolders for sorting/organising eg: by year and folder. Archive options are set up on a per account basis.

• https://support.mozilla.org/en-US/kb/archived-messages

Please note imap mail accounts show a view of what is on the server, so imap folders cannot be deemed as a separate independent copy on your computer. In effect, the folders on the server are one and the same as the folders in an imap account. If you 'move' any email from an imap folder to 'Local Folders' mail account, it is usually moved off server.

This can present an issue with a server like 'gmail' as the 'label' will get removed, so no longer appearing the folder, but it may still on server in the 'All Mail' folder. So it is still occupying space on the server.

Imap mail accounts can download just headers or full copies and this can be done on a per folder basis. If only headers are downloaded then when you select to read an email, it is retrieved from the server and stored in a temp folder on computer to facilitate viewing. It is not stored in Thunderbird. This means it does not use up space on your computer for storage. It also means you cannot view any of those emails without internet access to the server. The emails are stored on the server. If you were to look in the profile folders for the imap account you would only see *.msf files which are an indexing file used by Thunderbird. It does not contain emails. The set up determining what is downloaded is set up in the imap Account Settings > 'Synchronise & Storage' setting. See info:

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

If you need to perform a backup then you need to ensure you have downloaded full copies. This will show as mbox files (no extension) with same name as folder in the profile folders alongside the *.msf files.

Why did you see only *.msf files in 'Local Folders' ? Because you did not have a full copy downloaded, you only had headers and so you were basically archiving a load of headers. As these *.msf files are in 'Local Folders' and not an imap account, it is not possible to synchronise with server, so email content cannot be seen.

My advice on how to store good copies in Local Folders is written below, but be aware that others may say it is ok to set up Archives as you have done, but you really do need to be very sure you have a fully downloaded copy to start with and also suggest you do not have any Anti-Virus scanning Thunderbird files or scanning downloading files as they may interupt the process causing corruption or loss of data. It will auto remove off server because you 'moving' not 'copying', so if you do not have a good copy, all may be lost.

Ideally set up the imap account to use it's own 'Archives' folder. Then every once in a while get copies of those 'archived' emails into Local Folders account, so you can create space on server or just to have more than one copy stored on server.

Safe way of ensuring you have good copies in 'Local Folders'. Make sure all imap account folders are set up to download full copies. Choose to go into Offline mode and synchronise all folders so you are sure you have up to date copy. File > Offline > download/synch now select 'Mail messages' select 'Work offline once download and or synchonisation is complete. Click on 'Select' and make sure all folders and sub folders are selected - this should have already been done for each imap account in Account Settings, but worth a check - click on Ok Then click on 'OK' to commence process.

Once in 'Offline' mode... Why Offline ? If getting copies of a load of emails from one mbox file to another mbox file, it is better if the file cannot continue to synchronise with server - just less risky. Highlight batches of emails, right click on highlighted emails and use 'Copy to' and choose appropriate folder in Local Folders mail account. If for any reason the copy fails then at least you still have the original, so can repeat the process. BTW...if you can read email in Offline mode then you know you have fully downloaded copies.

I prefer to keep 'copies' of important emails in an 'Archives' folder in 'Local Folders' mail account which I handle manually rather than opt to use it as the auto 'Archives' folder for imap accounts. Once I have copies that I can read in 'Offline' mode, I know I have a full copies of everything, then I'll go back into 'Online' mode (quick method - in bottom Status bar - far left - click on icon) and delete the original still in imap folder, so it gets properly deleted off server. Finally, I would compact the folder(s) to ensure all hidden marked as deleted emails are removed and my files is smaller and tidier and less prone to getting corrupt.

I usually take the opportunity of creating a backup at this point as now I only have a copy on computer. Exit Thunderbird and copy the 'Thunderbird' folder to an external drive.

• C:\Users\<Windows user name>\AppData\Roaming\Thunderbird

Hope you find this info useful.

Thank you very much for your excellent and detailed reply! You clarified what options are available and I appreciate your advice on how I could do it better! You should consider adding your reply to the online help page! :-)