Is that account IMAP. It sounds like it and you have not considered the syncronised basis of IMAP mail accounts. ie delete on the server means implicitly it is also deleted locally.

I know that, for this reason I created a filter that automatically copy the email on local folder, it worked very well since September than the copied email are empty, either you see only the object but no content other you see a list of empty entry, with only the sender.

I am wondering if it's only an index problem, but I don't know how to test it or if a Thunderbird problem and it deletes thousands of email without warnings. The Pc has plenty of free space.

TIA

re: I use Thunderbird to store loacally some email from gmail and delete it from the online server.

If you create a POP gmail account then all emails get downloaded into INBOX and auto stored locally, so no filter needed to copy anything, Use filters to organise the emails in pop account folders.

re :I am wondering if it's only an index problem, but I don't know how to test it In 'Local Folders' -

• right click on relevant folder and select 'Properties'
• Click on 'Repair Folder',
• click on 'OK'

The index then is rebuilt based on what is actually stored in the mbox file.

When you download emails into the Imap account, have you got it set up to download full copies? Suggest you check: Account Settings > synchronisation & Storage for the imap account. select 'Keep messages in all folders for this account on this computer' Then click on 'Advanced' button and make sure every folder is selected.

Also select 'Synchronise all messages locally regardless of age'

re: Filter that copies: Does it just Copy to a folder OR have you also set it to Copy and Delete ?

Do you allow your Anti-Virus to scan:

1. incoming mail
2. any file that gets opened

if yes, then it's possible the Anti-Virus can intervene and take over temp control as it scans an incoming message. When saving downloaded email to a file eg: a file in the Local Folders , if AV is scaning opened files, it also can cause an interruption in the process.

It's often advised: Access Anti-Virus and set up an exception to not scan and folder or file in your Thunderbird profile. eg: C://Users/username/Appdata/Roaming/Thunderbird folder

Even if it found something, you should never allow a fix as AV's have no idea it's not just one email, that file may contain hundreds of emails and a fix could mean a total loss. There are other ways to check for something. Emails are ok providing you do not allow remote content, do not click on links that you have not checked as good links and do not open attachments just out of curiousity when you have no idea who really sent it. Often compacting folders removes old traces of previously deleted emails eg: Spam etc.