Today I opened Thunderbird, where I have two email accounts, and found out that the inbox folder of one of them was not showing the content of my messages, except for those it had just downloaded.

This is often what happens when anti-virus software is messing with Thunderbird mail files - they get corrupted.

In order to avoid this: Create an exception in your anti-virus software for the Thunderbird profile folder, so that the anti-virus real-time scanner will not scan it. http://kb.mozillazine.org/Profile_folder_-_Thunderbird

Don't let your anti-virus software scan incoming and outgoing messages.

Don't let your anti-virus software scan attachments.

Don't let your anti-virus software intercept your secure connection to the server.

Remove any add-ons your anti-virus software may have installed in Thunderbird.

Also see http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Anti-virus_Software

Is there any way to bring back my emails?

You'd need to restore them from a backup you've created before.

christ1 said

Don't let your anti-virus software scan incoming and outgoing messages. Don't let your anti-virus software scan attachments. Don't let your anti-virus software intercept your secure connection to the server.

But then whan about security? Is there any way malware can get on my computer via emails without me opening any attachments/links/whatsoever? By the way, I made the antivirus scan the PC because I saw some strange behaviors, so it didn't mess with Thunderbird by its own initiative. I don't know if the virus was in Thunderbird folder because I got it via email or for other reasons.

You'd need to restore them from a backup you've created before.

Oh well, I guess they are gone then, because I don't have a backup. Lucky me than they weren't really important.

I don't know how AVG treats infected files, but sometimes they put them in quarantine instead of deleting. In that case you might restore it.

But first, make an exception in AVG for your profile-folders Second, take care of your existing INBOX-emails as the old file might overwrite it.

Then I would move and rename the old inbox to local folders, esp if its an imap-account. If you know what email attachment that holds the virus you can delete it and compact that folder and empty trash.

But then whan about security? Is there any way malware can get on my computer via emails without me opening any attachments/links/whatsoever?

The short answer is, no malware cannot get on your computer as long as you don't deliberately open attachments and execute them.

The best protection still is to use your own brain, and be sceptical about unsolicited attachments. Don't open attachments you haven't explicitly requested.

Thunderbird doesn't carry out any embedded Javascript code in messages. Viewing messages in plain text instead of HTML is an additional protectection.

And you're still protected by your anti-virus real-time scanner when saving attachments to disk outside of your Thunderbird profile.

I made the antivirus scan the PC because I saw some strange behaviors, so it didn't mess with Thunderbird by its own initiative.

In that case it doesn't make any difference who or what triggered the scan.

I don't know if the virus was in Thunderbird folder because I got it via email or for other reasons.

An attachments is part of the message you received. If there was a malicious attachment it certainly was 'in a Thunderbird folder'.