Saving Locally Cached IMAP Folders
To backup and save locally cached IMAP folders to protect against a loss of data on the upstream IMAP server.
- Open Outlook
- File Menu
Open & Export
Export to a file
Outlook Data File (.pst)
- Select mailbox folders
- Give file destination and click finish.
This is to save a selection of messages
- right click on "Local Folders"
- "new folder", call it "saved"
- right click on the just created "saved" folder
- "new folder", call it "inbox"
- click on 2-screens icon in lower left hand corner of Thunderbird window to go into offline mode.
- choose "download later" if server is unavailable
- open inbox, select messages to save.
- drag them onto "Local Folders", "saved", "inbox"
- repeat above for "sent" and any folders into which you have saved mail
Use a 3rd Party Add-On Utility
To export files using an add-on utility https://support.mozilla.org/en-US/questions/988941.
This is the add-on https://addons.mozilla.org/en-US/thunderbird/addon/importexporttools/
Use file system tools directly
To export all folders using file system tools see https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer