Unfortunately, PST is a proprietary format not supported by most mail programs...

Do you still have access to Microsoft Outlook on any system? If so, the "simplest" solution is to connect Microsoft Outlook with an IMAP server -- this will show up as a separate set of mail folders -- and copy all of your old mail to that server. Then you can connect to that server using Thunderbird to work with it or download it. Gmail is one example of a free mail provider that offers access using IMAP.

If you no longer have access to Outlook, but you have Windows 7 or 8, or a recent version of MacOS X, you may be able to use a 30-day trial of Microsoft Office to do the conversion. I haven't checked on whether that's possible, but you could explore from here: http://office.microsoft.com/en-us/try/

You may find products or services on the web that convert PSTs to other formats; I don't know whether those are reliable.

Dear Google/Thunderbird team! This is a highly insufficient solution - there must be a way to secure all mails outside Thunderbird! I have to setup my pc and I am not willing to make additional effords beside the work a new setup requires.

Now I have to return everything to gmail, setup the pc, install Thunderbirds an to order some x-thousand mails AGAIN!

I like your products, but TB is really NOT my favored email client!!!

Hi Paddy12, I don't understand the connection between your problem and the original problem.

Hi! I want to save my emails which are stored with thunderbird, because I have to delete my hdd. How can I do this?

Thanks!

Hi Paddy12, could you check this article and see whether it is useful: Moving Thunderbird Data to a New Computer.