Follow these steps to import an archive (.pst) file into O365:

  1. Start Outlook.
  2. Click "File."
  3. Click "Open."
  4. Click "Import."
  5. Select "Import from another program or file."
  6. Click "Next."
  7. Click "Outlook Data File (.pst)."
  8. Click "Next."
  9. Click "Browse" to choose the file to import. Usually, you can find this by browsing to “Your documents,” then “Outlook files” - or your “G drive."
  10. Click "Open."
  11. Under Options, click "Do not import duplicates" (nless you want the imported information to replace or duplicate items that are already in Outlook).
  12. Click "Next."
  13. Select the folder that you want to import. (If you want to select everything in the .pst file, select the top of the folder hierarchy).
  14. Leave “Include subfolders” selected if you want to import all subfolders within your selected folder. (If you do not, unselect it). 
  15. Click "Finish."