If you have Thunderbird set up with an IMAP account: Thunderbird does not delete emails unless you have set it up to delete via settings or filters or manually delete. If emails have been deleted on the server and put into trash, then an imap account can only display what is on server. You are saying - you are not even touching anything and you start to see emails getting put in the trash. So check your settings: * Account Settings * Select 'Synchronisation & Storage' * Select 'Synchronise all messages locally regardless of age' * Select 'Don't delete any messages' Do you have any 'Message Filters' which you created? If yes, then please check to see if you have any filters which put emails in the Trash. You may have set a filter which can be applied to a lot of emails. Check the filter log to see what it says. Check 'Tools' > 'Activity Manager' Does it say 'Deleted x number of messages from Inbox' The following is the most common cause of this type of problem: Do you have any other device accessing the server ? eg: Another computer, laptop, phone ? If you have any other means of accessing emails eg: phone and it connects via a pop account then if it has not been instructed to leave messages on server, it will download and delete of server. Or if you had a phone accessing via Imap and you deleted any emails then they get deleted off server. Another problem is if you have another email client running in the background. I have come across a person who used to use Outlook. They thought they had removed the account from outlook. But upon further investigation they discovered much to their supprise that Outlook was working in the background. It was still downloading emails. The account was still live and kicking, but it was a pop account which downloaded and deleted emails off server or had other settings like delete after x days. The point being no one was aware of this. You mention 'Outlook' so please check to see the account has been removed. If emails are being deleted off the server and put into the server TRash then any IMAP account will get auto synchronised to match what is on the server. So it can look like emails are being deleted when in reality they were already deleted by something else accessing the server. HOW TO GET A BUNCH OF EMAILS MOVED TO ANOTHER FOLDER Select trash folder Select first email in list Use Ctrl+A to highlight all emails Right click on highlighted emails and select 'Move to' and select account Inbox folder. OR do it in batches Select trash folder Select first email in list Press and hold down 'Shift' and click on another email - all emails in between get highlighted, so you can do it in chunks. Right click on highlighted emails and select 'Move to' and select account Inbox folder.