OST to Office 365 migration is a challenging task. Outlook has no option to import OST files. But you can import PST (*.pst). Here is best OST to Office 365 migration tool that works on both Mac & Windows for you.
OST Data
OST is a cached copy of your exchange data, stored locally on your Windows PC (by default, the file is inside: (C:\Users\user\AppData\Local\Microsoft\Outlook). It gets synced with the server data when the internet connection is there.
By the virtue of the fact that it is offline and stored locally, it is safe from any network failures or server connections.
There are many cases where OST files might be left alone and undamaged, while the email accounts and data is damaged.
Deleting original email account can also make OST file inaccessible, but not delete it. An OST is only linked with the original account, without which, it is often inaccessible on its own.
OST to Office 365 Migration
Our guess is, if you are here reading this, you too have an OST file that you want to get back into Office 365 Outlook. And if you yet haven’t tried importing it traditionally, sadly we need to tell you that it is not possible. There is no way you can import OST to Outlook manually. It is an internal file that functions automatically.
If you create a new dummy account with IMAP and try to replace the new OST file with your old one (the one with all the data), it still won’t work. Outlook will give an error saying the file in Profile/Identity folder belongs to a different account.
The bottom line: the only way to get OST to Office 365 is by converting it to PST.
There are many tools and converters that in one way or another do the same. But most of them result in data fragmentation and loss. OST is a complex file and to recover everything with the structure intact, you need a sophisticated tool with smart algorithms. Think images, attachments, headers, contacts, links, and other details – not all of them will be safely processed by a common denominator tool.
OST to Office 365 Migration Tool
“OST Extractor Pro” is what you want if you care about the information and want to convert it to PST cleanly.

It features next-generation algorithms that run deeper and wider than any other solution. This provides the output files that has nothing changed from the original except the format. The brilliant mechanism at work here will keep folders and their order, images and all graphical contents, email addresses, and even Unicode headers preserved.
- Natively supports bulk conversion
- Also converts OST to Apple Mail, MBOX, and EML
- Tech support is always read to assist you day or night
- Standalone, desktop-based, and dedicated utility
- Available for Windows and MacOS (one license for both)
- Fast and steady
How to Migrate OST to Office 365
- Get ‘OST Extractor Pro’ for Mac or Windows.
- Install and launch it.
- Click on “Add OST”
- Browse and select a single or multiple OST file, the click on “Add”.
- Check Optional Settings:
- Ignore Empty Folders
- Check/Uncheck Folders from Preview that you want to convert.
- Now select the output format as PST file (*.pst) for Office 365. Below are other output formats:
- Apple Mail, Addressbook, Calendar (iCal)
- Thunderbird/Postbox, *.ics, *.vcf
- *.mbox , *.ics, *.vcf
- *.eml , *.ics, *.vcf
- Then click on “Convert“.

Free Trial for OST to Office 365 Migration
If you want to try it, go with the trial version first. Downloading is free and without any signup process.
It is simple to use from the get-go. Needs no complex setup or configuration.
You can begin the trial version within the next minute and get to see it “in the flesh”. Get the full version of this OST to Office 365 migration tool for safe and secure data conversion.