If you want to import PST to Office 365, According to my experience use the migration tools Because is you are using the third party tool you can import PST data to office 365 very easily and with proper security. For the PST to Office 365 migration you can try, Shoviv PST to Office 365 Migration Tool. I also used this tool. The tool easily imports multiple PST data to Office 365, Live Exchange, EML, and MSG formats and also recover corrupted and damaged OST/PST data files to new PST/OST file. But its all your choices so first Download its free demo version and check the all features and quality of the tool and also import the first 25 data items per folder from PST to Office 365.

More details, visit:- Import PST to Office 365