Right click the folder, select properties and then the repair button to get the index (MSF) and data in sync. You could also delete the MSF with Thunderbird not running. Same end result.

It is recommended that you not allow anti virus to scan your mail storage files for exactly this reason. They do major destructive actions for basically Zero return.

Thunderbird mail is stored as a text file. there is no way any nasty can escape, because text is simply not executable. Thunderbird does not run scripts in messages, so there is no way to download stuff from a remote web site. The script does not run. If the threat is in an attachment (it is also stored as text (Mime encoded) so it does not represent more than a latent threat. Should you choose to open the attachment Thunderbird will decode the file and save it to the temp folder where your anti virus will scan it before it is executed.

The only "threat" email in Thunderbird has is the theoretical risks associated with fetching remote images, but scanning before the even will not help with that.

Hi Matt,

Thanks for taking the time to reply.

Sadly the "repair" option won't/doesn't work. It's not that the .msf and mbox files have become unsynchronised, but that the mbox file no longer exists at all.

The Inbox.msf, Inbox.sbd and Inbox.mozmsgs files all exist, but Inbox(with no file extension has been deleted (inadvertently) by me/AVG.

I've now accepted that I can't recover the original mbox file.

QUESTION: Will the Inbox mbox file be recreated automatically by Thunderbird if I "Get messages"?

Thanks for the info that I can safely add the Thunderbird message storage tree to AVG exceptions, as that will solve the ongoing problem.

I've been using AVG for about 10 years now, and never had a problem before.

I can't find any info online about the FACEBOOK-A threat that AVG is reporting.

All very odd!

Have used the "Send for analysis" button to send the false positive files to AVG.

I've been saving my messages on the Yahoo server as a back up, and will be researching the deletion of the popstate.dat file to force Thunderbird to re-download messages from the Yahoo inbox.

Above details included for anyone who has the same problem.

an inbox should be created as soon as it is needed. You are not the first person to be struck by AV software deleting there entire inbox.

Now we are into personal stuff.

The Mozmsg stuff... It almost doubles the size of your profile and exists for the sole purpose of allowing the windows search to index your mail. Unless you are in the habit of using windows search to search mail it is an option that should be disabled in my view as it saves disk space, reduces duplication and if like me you do a backup, make that more manageable.mozmsg is the folder and mozeml files are what inhbit the folder. A modified standard EML that is missing any attachments and anything after, i think, the first 40kb of the email file (that means some are complete) The unfortunate part is turning off the option deletes nothing, so you have to manually delete the mozmsg folders.

Thanks again Matt - Lots of helpful responses in your message.

Info that may be useful for others suffering the same problem:

How I recreated my Inbox ...

I closed Thunderbird down

I moved the inbox.msf file to another folder, so that the headers would no longer appear in the Inbox. (If you clicked on a header entry it would say file not found, so the headers alone were of no use.)

For reasons I have yet to fathom, I sometimes find a complete copy of my Thunderbird Inbox, as a folder called Inbox, within another folder. Fortunately this had happend just a few weeks ago, so I had a copy of my Inbox as it was on 3 Mar. (Note to self - hoarding tendencies are sometimes useful!)

I logged into the Yahoo online system, and moved all the messages in my Yahoo inbox dated before 3 Mar into other folders. (Note to self: The decision to tell Thunderbird not to delete messages on the server after they're downloaded was an excellent one!)

Back in the Thunderbird profile folder I deleted the file popstate.dat, which holds details of which emails have already been downloaded from the server.

Back in Thunderbird I hit the "Get Messages" button, which downloaded all the messages sitting in my Yahoo server inbox. Due to my previous actions, this was all the messages I'd received from 3 Mar onwards. This action created the Inbox.(noextension) file which, between us, AVG and I had managed to delete.

I then copied all the messages from the 3 Mar Thunderbird Inbox copy, into the main Inbox.

The only thing left to do now is to sort out some message duplication as a result of the recent download duplicating previously received messages that I'd already filed in folders other than the Inbox.

A trivial problem compared to where I started!

That's Thunderbird mostly sorted out.

I then went into AVG and set up the location of the "Mail" folder in my Profile as an "Exception". This automatically covers subfolders. So AVG won't scan the Thunderbird data files, and throw up more false positives.

I get that the mozmsgs can be seen as a waste of space. However, due to another ongoing Thunderbird problem I've had, I'm going to hang onto them as a backup. Sometimes, when I move a Thunderbird folder to somewhere else in the folder tree, I discover that the message file associated with that folder arrives at its destination with a file size of zero, ie all the messages are lost. NB I am not raising that as an issue here. Just saying!

If I have the .mozmsg version of the file, at least I have something left to reference. Based on recent experience, I clearly need as many backups as I can get!

Speaking of which, I have never backed up the Thunderbird message file area in the past, but as the result of your message may consider doing so in the future.

Much appreciation to Matt for his assistance.

It's been an education!