Thunderbird automatically stores emails in this location: C://Users/user name/Appdata/Roaming/Thunderbird/Profiles/profile name In the 'profile name' folder: 'Mail' folder stores all pop account name folders and the 'Local Folders' mail account. 'ImapMail' stores all the imap mail account name folders. In the pop or imap account name folder or the 'Local Folders' folder - Emails are stored in mbox files. Those files do not have any extension, but do have same name as folder eg: Inbox, Sent etc. Those mbox files can be opened using a Text editor eg: Notepad, so you can check the contents. Downloaded Emails get appended to the file, so added one after the other. The oldest will be at the top. If you see files with a .msf extension, this is just an index file used by Thunderbird and it does NOT contain emails. If you see folders with a .sbd extension, this means there were subfolders. Those *.sbd folders may contain mbox files. Perhaps you 'Archived' those oldest emails, so there may be a 'Archives.sbd' folder you could check. mbox files can be copied into the current Thunderbird profile, but must be put into the 'Local Folders' folder. You must exit Thunderbird before this is done. I've added an image as an example which explains what mbox file looks like and how you can copy and paste into current 'Local Folders'.