It is likely you are talking about an imap mail account which shows a virtual copy of what is on the server. Imap mail accounts store emails on the server. The imap account folders synchronise with server folders to show contents/emails in Thunderbird. Connecting with an empty server will show empty folders. Usually, when it is known that you will stop using a particular email address or server and all your emails are stored on the server, it is necessary to get copies off the server and stored in a location you can continue to access those emails. So, you would synchronise folders for offline use to get full copies of emails downloaded into Thunderbird and then in offline mode, get copies put into suitably named folders in the 'Local Folders' mail account, so that emails are stored on your computer and not within the imap mail account. Hopefully, your backup will have copies of synchronised folders which will have mbox files containing emails in the imap mail account name folder eg:%appdata%/roaming/Thunderbird/Profiles/profile name/ImapMail/imap mail account name mbox text files do not have any extension and have the same name as the folder name eg: 'Inbox'. These are only created if you had full copies of emails downloaded. If you see 'Inbox.msf' these are just indexing files and do not store emails. If you see 'Inbox.sbd' folder then it means you had subfolders in the Inbox. The 'Inbox.sbd' folder may contain mbox files and index files. Use this addon extension: ImportExportTools https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools/ import mbox files from the backup ... ''I had backed up my %appdata%/roaming/Thunderbird director so I have my profiles.'' eg:%appdata%/roaming/Thunderbird/Profiles/profile name/ImapMail/imap mail account name folder Import into 'Local Folders' mail account. Once emails are in 'Local Folders' create another backup, so it is up to date.