Is this a pop or imap account ? Do not know? In Account Settings, select the 'Server Settings' for the account and look on the right side. Does it say 'Server type': 'Pop mail server' or 'Imap mail server' ? If imap: Logon to your webmail account via a browser eg: Firefox and see if emails are in the Inbox server folder. What do you see? What server are you using? eg: BT, comcast, gmail ? Possible reasons for loss of emails: 1. Index has gone squiffy and is out of synch with Inbox mbox file that contains emails. * Right click on Inbox and select 'Properties' * click on 'Repair Folder' * Click on OK 2. You have an Anti-Virus which is allowed to scan your Profile and it did not like the 'Inbox' file, so it might have quarrantined the file or attempted to fix it. Anti-Virus programs do not understand that the Inbox mbox text file can hold many emails, so could end up deleting the lot in fix attempt. That would explain why Index is out of synch and also why a repair folder did not find emails. You would need to check your Anti-Virus quarrantine to see if you can rescue the Inbox file. But either way I would advise that you do not allow AV to scan any profile folder or if you do then do not allow it to fix anything. What Anti-Virus do you use ? 3. If you use imap - did you logon to server webmail account and delete anything ? If yes, then an imap account cannot show what does not exist. 4. Are emails in the 'Trash' / 'Deleted' fodler - if yes, then put them back into the Inbox. Do you see emails in all your other folders? What OS do you use? eg: Windows 10, MAC, Linux ? What version of Thunderbird do you use? Not sure? In Thunderbird - Help > About Thunderbird will tell you what you are currently using. I