Manually this is not possible because this will take long time to search and remove duplicate nsf items one by one. If you seem you have bunch of duplicate .nsf files and have no idea what should do then download SysInfoTools NSF Duplicate Remover App. This application auto-detect the duplicate nsf files in Lotus Note saved folders.

Hi Paul Christie,

 while hearing about your issue, i'll found its interesting and try to find solution for the it, after searching and checking lots of option i found an alternet solutions. first while you are going for manual conversion its not easy like its sound, its waste your lots of time, as per third party i didn't find lots of option but i found Softknoll NSF to PST Converter i have't use this tool but heard about this on google you can try this tool