If you are failed to convert PST to MBOX file for mac , then you can easily download this tool, It supports all MS Outlook versions up to 2016 (32 and 64 Bit). To get more Info Visit now : http://www.pstfile.org/mbox/
I found a similar conversion before which is near to resolve with some good solution for Export PST to MBOX file , It gives best result as well as fully protection your file , To get more details : http://www.pstfile.org/mbox/