Having MS Outlook installed in your computer, when user need to import data from other email client like Thunderbird, MAC Outlook, WLM, etc. to Outlook, they can do it manually using Import/Export feature. But sometimes you may find it difficult since the the manual solution is . However there are some third party tool available in the market like: SysTools EML to PST Converter, which I would recommend to you on the basis of my personal use. It allows user to export by selecting the desired eml files as a pst file format.