If you have an anti-virus product either scanning Thunderbird folders on startup or scanning incoming mail then it is possible the AV is causing this issue. Suggest you access AV and stop it scanning any Thunderbird folders on startup and also stop scanning incoming mail. It will still scan any attachments you open. Thunderbird does not show remote content by default. Do not disbale AV as then the default one will take over; you need to set up so not scanning Thunderbird folders. Then Check to see if this is just an index out of sync with actual folder contents. * Right click on Inbox and select' Properties' * click on 'Repair folder' button * click on OK * select another folder and then reselect 'Inbox'. If repairing index does not work..... It is also possible you have a corrupted Inbox. Check to see if emails can be recovered: Make hidden files and folders visible: * http://kb.mozillazine.org/Show_hidden_files_and_folders In thunderbird * Help > TRoublshooting Information * click on 'show folder' a new window opens showing profile folder name * '''Close Thunderbird now - this is important''' you should see 'Mail' and 'ImapMail' folders If POP mail account: * click on 'Mail' folder * click on pop mail account name If Imap mail account * click on 'ImapMail' folder * click on imap mail account name you should see the 'Inbox' mbox file - it has no extension. If IMAP mail account and no Inbox (no extension) mbox file, then emails were not downloaded and stored in Thunderbird. * Open the 'Inbox' (no extension) file (not Inbox.msf) using Notepad. emails are written to the file, one after the other in the order downloaded. So oldest will be at the top. Each email will start with these lines: this is an example * From - Sun Dec 28 18:14:40 2014 * X-Mozilla-Status: 0001 * X-Mozilla-Status2: 00800000 Use 'Edit' > 'Find' Starting at the top use the look for this line: '''X-Mozilla-Status:''' 0001 It will probably have different numbers on different emails. Make sure each '''X-Mozilla-Status:''' has the number '''0001''' * edit the number as required working down through the document. * Save the file. * delete the 'Inbox.msf' file. A new one will be auto created. * Restart Thunderbird. that should get any recoverable emails back in Thunderbird Inbox. Whether emails are recovered or not, I would suggest you now do the following on the Inbox. * Move all good wanted emails out of Inbox into other suitable folders for organising and storage. * Delete any emails you do not want. When Inbox is empty: * right click on inbox folder and select 'Compact' * right click on 'Junk' and sselect 'Empty Junk' * right click on 'Junk' and select 'Compact' * right click on 'Deleted/trash' folder and select 'Empty deleted'