Then when the Thunderbird imap account synchronises with server (after the pop account), the email in imap account will disappear because it does not exist on the server. If you are also running a POP mail account to same email address from any device ( Thunderbird, another computer, phone etc) and it downloads the email, it could be deleting the copy off the server. However, there are also settings to delete copies off server when deleted from pop account. There are settings within a pop account to force a copy to be left on the server. By default, the server will delete the copy on the server after the email has been downloaded to a pop account. POP mail accounts can only access and download from the server Inbox. There will be a 'Message Archives' section stating the name of the folder and the account. This opens the 'Account settings' window.

Right click on the imap mail account name in the Folder Pane and select 'Settings'.How to find out what folder is set up to contain archived emails. Select the folder and click on 'Subscribe', then click on 'OK'.Right click on the imap mail account name in the Folder Pane and select 'Subscribe'.

You may need to subscribe to see that folder. If you selected an email to view and then pressed the 'A' key, this is a shortcut key to auto archive the selected email and will auto archive the email into where ever you have set it up to archive those emails. It is possible you accidentally archived the emails. IMAP mail accounts only show what is on the server because imap folders synchronise with server folders. In most cases, it is rarely the problem with the Thunderbird program itself and so uninstalling and reinstalling the program will usually not make any difference.

Why do emails disappear after 1 month