I am not aware of any fee email client that can support pst files directly, but I believe in Mozilla Thunderbird, a free email program, a PST file can be imported after a file format conversion. Thunderbird supports MBOX file format. When a PST file is converted into MBOX then it can be imported into Thunderbird. However I think that you need a 3rd party converter such as Stellar PST to MBOX Converter. However this is not free.
http://www.stellaroutlooktools.com/scan/pst-to-mbox.ph
Of course there maybe other conversion apps out there that are free.
You can also get a converter for .msg files which as I mention you can drag out individual or multiple messages from Outlook. Again it's not a free converter.
http://www.importmsgtothunderbird.birdiesoftware.com
It's not something I use myself so that's about all I can offer.
Edited by deleted (Thu 26-Mar-15 22:02:12)