''re: several old emails in the inbox didn't seem to have any content. I could see the sender and subject in the list of emails, but nothing in the quick-view window. '' This was a sign of a corrupted folder. ''re Today I was seriously annoyed by this, and attempted the "repair folder" option. That abruptly washed away ALL the email in the entire inbox'' No. This only forced a reindexing to show was actually in the Inbox. ''re : the inbox represents an archived year of my life and work'' As you had loads of important emails in that single file, I presume you have made several backups over the years. You could use the backups to reinstall any lost emails. '''ImportExportTool '''is a good addon for helping to import both .eml files and mbox files (depending upon how you backedup the emails) back into Thunderbird. * https://addons.mozilla.org/en-US/thunderbird/addon/importexporttools/ '''General info on Inbox folder:''' An Inbox folder should be used as an Inbox for incoming mail and shouldn't be used as a general store or archive. An Inbox folder displayed in the Folder Pane is actually an mbox file in your Profile Folder. Emails are stored in that file written one after the other in the order downloaded. When emails are deleted by you, the email is marked as deleted and from your point of view it disappears out of the Inbox folder and reappears in the 'Deleted' folder. In reality it is still in the Inbox folder just 'marked as deleted'. This allows for you to undelete it if necessary. When you compact your folders, those 'marked as deleted' emails are completely removed. This frees up space in the Inbox reducing its size and helps to maintain a healthy folder. As the Inbox folder gets more activity than other folders, compacting on a regualr basis is important. If you do not compact on a regular basis problems can occur. If compacting was run on a corrupted folder, it would have attempted to remove 'marked as deleted' emails, but if the file was corrupted and TB couldn't determine where a 'marked as deleted' email ended then it could delete good emails. See info on Compacting and why it is so important: * http://kb.mozillazine.org/Thunderbird_:_Tips_:_Compacting_Folders '''If the Inbox folder has NOT been compacted either manually or automatically then try this:''' Make hidden files and folders visible: * http://kb.mozillazine.org/Show_hidden_files_and_folders In Thunderbird Help > Troubleshooting Information * Click on 'Show Folder' button * Close Thunderbird now - this is important * Click on 'Mail' folder * click on mail account name folder Look for Inbox file no extension (not Inbox.msf): How big is the file? Can you open it using 'Notepad' ? If yes, you can open it in Notepad Look for this email header - you can use the 'Edit' > 'Find' * X-Mozilla-Status: '''0009''' then edit the '''0009''' to say '''0001''' work through the document changing all of those headers. then save and close the file. Look for and Delete Inbox.msf file. Close Window - top right X Start thunderbird. All those emails marked as deleted - 0009 will become marked as new unread mail - 0001.