Just to clarify Are you talking about your outlook .pst files used with Outlook 2007? If so, using the import export function in Outlook (either 2003 or 2007) will import .pst files created in 2007. The correct way would be: Open the Outlook 2007. Go File then Import Export and Export as a .pst Save it to an easily accessible location (i.e Desktop or a USB if it's on another PC) Go to Outlook 2003 File Import Export Then import the .pst If it is an ost file from an exchange server then there are some OST to PST conversion tools like OST to PST Converter Kit. https://www.converterkits.com/osttopstconverter.html Otherwise you really need to open the pst files on a machine with outlook07 in order to do the export.