What is the safest way to import an OST file into Microsoft 365?

[niamhmurphy]

I'm planning to migrate an Outlook OST file to Microsoft 365 and want to avoid any data loss during the process. The mailbox contains important emails, attachments, contacts, calendars, and custom folders that need to be preserved.
So, I need to import an OST file into Microsoft 365. What is the safest method?

 

[Jameswhite]

To import OST file to Microsoft 365, the safest way is to backup OST file first and verify your mailbox after migration. If your OST file is still linked to Outlook, you can export it as a PST file and then import the PST file to Microsoft 365. I tried this method, but it is not very convenient for inaccessible or multiple OST files. So that's why now I prefer to use reliable data importer tools like the GainTools Cloud Importer, and it really made things easier. It worked great for my migration, importing all my emails, attachments and folder structure without losing any data.