DBX to PST conversion is required if you want to move old e-mail messages from free Outlook Express into Microsoft Outlook.
Both these email database file formats .dbx and .pst are used by Microsoft products. An obsolete Outlook Express which was a Windows native free email client understands dbx (Outlook Express email folder file) format and saves all the emails data into it. Whereas Microsoft Outlook understands PST file format and hence understands only pst (Outlook personal storage table file).
There are many software tools available, but you can manually convert DBX to PST by using Windows Live Mail import and export feature.
Programs like DBX to PST Converter from Systools are specially created to help users to convert various e-mail folders from Microsoft Outlook Express (*.dbx files) to more advanced Microsoft Outlook email client (*.pst file format). This can probably be done also with the free version of the program, but there may be some limitations.