emails are stored in mbox text files. They have same name as folders but no extension. If you have a backup of those mbox files then you can import them back into Thunderbird. But you need to import them into 'Local Folders' account. Getting mbox files that contain emails into Thunderbird can be done manually via profile folders OR use this addon 'ImportExportTools NG' * https://addons.thunderbird.net/en-us/thunderbird/addon/importexporttools-ng/ '''To do it manually:''' In Thunderbird * Help > Troubleshooting Information * Under 'Application Basics' - half way is Profile Folder - click on 'Open Folder' It opens in a new tab showing the contents of your profile name folder. * At this point Exit Thunderbird - this is important. * Click on 'Mail' folder to see contents * Click on 'Local Folders' folder to see contents. keep this view open because this is where you paste / put copies of backup mbox files. Make sure to rename the files if they are going to clash with any current folder name. When you restart Thunderbird, those mbox files will appear as new folders in the 'Local Folders' account. If you need/want to get them back into an imap mail account Highlight a batch of emails - not too large as there maybe a limit on what can be uploaded back onto the server in a given period. Right clickon emails and choose 'Copy to' and select the relevant imap folder. REpeat until finished. Mind you - you could just leave them in 'Local Folders'. '''Using addon ImportExportTools NG:''' * https://addons.thunderbird.net/en-us/thunderbird/addon/importexporttools-ng/ '''''How to install addon:''''' * https://support.mozilla.org/en-US/kb/installing-addon-thunderbird Addon menu is inserted into right click context menu of folder and account name. * Right click on Local Folders folder and select 'ImportExportTools NG' > 'Import mbox files' > choose relevant option. The one which says .sbd structure means - if selected item it has any subfolders then import at same time.