Imap accounts tend to auto subscribe and show server default folders that cannot be deleted such as Inbox, Sent, Spam, Drafts, Trash.

In Thunderbird, you can choose to 'Subscribe' to see folders or not, but some servers only allow this for non-default folders. Right click on imap mail account name in Folder Pane and select 'Subscribe' to see the available list.

Gmail keeps all incoming, outgoing and archived emails in the 'All Mail' folder. Gmail applies labels such as 'Inbox' in order to show emails in a more conventional 'folder' view. Gmail Archived means all labels have been removed, so email is only stored in 'All Mail'. When you delete emails they need to be put in the gmail trash folder. Gmail auto removes emails older than 30 days if they are put in the gmail trash, that means removed from 'All Mail' folder. If deleted, but not put in the gmail trash folder, then only the label is removed and the email is therefore 'archived'.

In gmail webmail account viewed via a browser, you can select which labels you want to make available for imap. Under 'Settings' > 'Labels' there should be checkboxes to select to 'show in Imap'.

In any webmail account you could do some preparation. EG: create new folder(s) and move older emails out of Inbox into those folders and then choose to not make those folders available for imap or in Thunderbird not Subscribe to see them So you could preset this before creating the imap account in Thunderbird.

Some servers use a gmail type of format - an 'All Mail' folder for all emails, others can be more conventional. Incoming emails are only stored in Inbox unless moved.

In Thunderbird, you can choose to only download headers or only download full emails or a mix based on name of folder. Downloading full emails will use more space. In Account Settings for the imap mail account, under 'Synchronisation & Storage'. Uncheck 'keep messages in all folders for this account' click on 'Advanced' button Any folder that is selected will download full emails, so uncheck all if you only want to download headers.

Good info here: https://support.mozilla.org/en-US/kb/imap-synchronization

under 'Account Settings' > 'Server Settings' Message Storage section. Advised to choose 'Clean up (Expunge) Inbox on Exit' This compacts the Inbox removing all traces of 'marked as deleted' emails. info on compacting: https://support.mozilla.org/en-US/kb/compacting-folders

Imap accounts store emails on server, so if you need to keep emails but get them off the server to increase quota, you would need to change settings to allow full download of emails for offline use. Then get copies put into 'Local Folders' mail account, before deleting the copy in the imap folder, which in turn will delete email off the server when you go back online. This does mean you now have full copies of emails in 'Local Folders' mail account so it will use space.

As the only copy is held on the server, if you need to create a backup and store backup on eg: external hardrive, so you have copies of emails, then you would need to get download of full emails.

Whilst in offline mode, change settings back to only downloading headers. Then exit Thunderbird and copy the 'Thunderbird' folder which will store everything, profiles, emails, filters, preferences, address books etc. The location depends on the OS. eg: Windows OS it is in the AppData 'Roaming' folder: C:\Users\<Windows user name>\AppData\Roaming\Thunderbird More info on other OS: http://kb.mozillazine.org/Profile_folder_-_Thunderbird

For emails that only downloaded headers: When you select an email, it is retrieved from the server and stored in a temporary folder to faciltate viewing. It is not stored in thunderbird.

To avoid excessive downloads at the start, go Offline, then add the account, enter the main details, then click Advanced config. where you can uncheck the box for Message Synchronizing in the Sync. & Storage section of Account Settings. Also, uncheck 'Place a copy in' in Copies & Folders as gmail automatically copies sent messages.

When you go back online, you can further reduce the (headers only) downloading by unsubscribing to All Mail and any other unnecessary folders.