I finally found a software that allows me to convert the Outlook for Mac 2011 back into Outlook for Windows 2010 PST files. It requires a two step approach: 1. Open Outlook 2011 for Mac and open a finder Window. Drag a directory from the left navigation pane in Outlook 2011 and drop it into the finder window. It can take up to a few minutes without any prompt of progress window. Once finished, you find a file named directoryname.mbox in your finder window. 2. Purchase and download the software MBOX converter from SoftLay. http://www.mboxconverter.com/ The software costs 69 USD. You can test it first by downloading a demo license that extracts only 5 email files. The MBOX Converter takes the mbox file created in step 1 as the input and converts it into a PST file, with all the directory and sub-directory structure of the original folder in Outlook 2011. Finally I have a working solution to port the Outlook 2011 message store back to Outlook 2010 if I have to. I previously used a local IMAP server, bit that process was too cumbersome and time consuming. I hope you find this tip useful.