If you use an imap account please make sure you have synchronised all folders to download full copies of emails and not just headers. See info: https://support.mozilla.org/en-US/kb/imap-synchronization#w_configuring-synchronization-and-disk-space-usage To perform a manual backup is easy and quick. In Thunderbird Help > Troubleshooting Information Under 'Application Basics' section click on 'Open Folder' button located to the right of 'Profile Folder' A new window will open showing the contents of your 'profile name' folder Exit Thunderbird now - this is important. The default location for storing profiles in Windows OS is: * C:\Users\<Windows user name>\AppData\Roaming\'''Thunderbird'''\Profiles\<Profile name>\ Go up the directory three clicks so you are in the 'Roaming' folder Copy the 'Thunderbird' folder and paste it into a suitable location eg: external harddrive. Backup completed. All profiles, mail accounts, emails, address books, message filters etc. Start Thunderbird. Should you ever need to use it, simply copy and paste the 'Thunderbird' folder back ino the 'Roaming' folder - obviously overwriting the current 'Thunderbird' folder if it exists. Remember to exit Thunderbird first. It is also possible to extract the mbox files (no extension) and copy them back, although if using imap accounts, you would need to copy paste them into Mail\'Local Folders'. Then after starting Thunderbird, you can copy emails back into the imap folders to get them back on server.