re :''When I clicked the "Repair folder" button on the Inbox folder, all emails from 2018 were gone. '' Obviously, something was wrong in the first place which prompted you to try repairing the index file. I'm always suspicious that an Anti-Virus is involved when an 'Inbox' mbox file seems corrupted and the Inbox.msf file has been ignored. This often means you see list of emails which looks ok because nothing is wrong with the index, but when you select them they are a blank because the index is pointing to nothing. Repairing the index means the index is erased and rebuilt based on what is in the mbox file, so showing it's true contents. Getting the index realigned with the actual list of emails. Rebuilding the index does not delele anything. The 'Inbox.msf' file is the index file and it does not contain emails. The 'Inbox' mbox file is a text file. When you download emails they are written to that 'Inbox' mbox file, one after the other, so oldest is at the top and newest at bottom. As this 'Inbox' mbox file is a single text document, it is not a wise idea to keep all emails in that Inbox folder. You would have all your eggs in one basket, so to speak. It is very risky to have all your emails in one simple text file. If you have an Anti-Virus product scanning files and it decides to try to fix that file, then you would lose everything because it is only one file. Hence it is advised you create other folders to store the received emails in a more organised manner. This means the emails are now kept in several files and this lowers the risk. Please try the following to see if there are any emails in the 'Inbox' mbox file which might be 'marked as deleted' and hidden from view. Exit Thunderbird first before accessing the profile folders to see mbox file. Open the Inbox mbox file using Notepad. Each email in a pop account will start with these lines: this is an example * From - Sun Dec 28 18:14:40 2014 * X-Mozilla-Status: 0019 * X-Mozilla-Status2: 00800000 followed by all the various headers and then the actual contents of email. I've included a couple of example images to help show you what I'm talking about. Starting at the top of the file use 'Edit' > 'Find' to help to look for this line: * '''X-Mozilla-Status:''' ( - NOT this line: X-Mozilla-Status2:) Make sure each X-Mozilla-Status: line has the number '''0001''' * Edit the number as required changing to say 0001 working down through the document. Take your time. * Save the file. * Delete the 'Inbox.msf' indexing file. A new one will be auto created on restart. * Start Thunderbird.