Migrating a PST into a new Office 365 Exchange Mailbox

I've upgraded a friend's email from using a POP3 server to Office 365 Business with Exchange. He uses Outlook as his only client. I exported all his old emails to a PST and then imported them into the new O365 mailbox. There are many folders that appear empty. He has 100s of folders and sub folders. I've tried this twice.

Could you suggest a better way to meet my goal?
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timgreen7077Exchange EngineerCommented:
How did you import the pst file to the o365 mailbox?
JohnMan777Author Commented:
Using Outlook I exported his old POP3 email to a .PST.

On his new computer I opened Outlook, configured the connection to O365 to his new Mailbox. I then imported the .PST from the other machine.
timgreen7077Exchange EngineerCommented:
Can you just connect the pst to the outlook client connected to the O365 mail. So open the outlook client with the O365 mailbox and mount the pst to that outlook client and then drag and drop the PST connect and see if that works.
JohnMan777Author Commented:
I would have to drag the contents of hundreds of folders from the attached PST to the new O365 Mailbox. Outlook doesn't support dragging folders that way. Only Items inside the folders.
timgreen7077Exchange EngineerCommented:
Perform a copy and paste and that way you can get the folders. There are only a few ways to get a pst imported into and o365 mailbox:

1. Drag and Drop or Copy and paste (slowest method)

2. Use Micosoft's recommended way by going to the following link:

3. Use a third party paid for tool for example the below (there are many options on the 3rd party software)

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