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Best Method to Import OST to Office 365 – Don’t Miss Out

Written By
Nick Rogers
Published On
February 23rd, 2023
Reading Time
6 Minutes Reading

This post will explain how to import OST to Office 365 account, including emails, contacts, attachments, calendars, tasks, journals, and so on. Microsoft 365 experts have verified and recommended all steps.

Importing OST to Office 365 is a crucial and complex task. It requires meticulous planning and precise execution, as the whole process of uploading an OST file might stretch out into multiple strenuous steps.

Microsoft 365, synonymous with Office 365, is the next step over the old system of Exchange Server. It has all the benefits and features of the previous system plus the improvements of an online entity.

But, to import OST to Office 365, we need to implement some roundabout methods, as Office 365 does not import OST files directly.


OST (Offline Storage Table) is a file that is a replica of the original data stored in the Exchange/IMAP server. It is an offline copy that routinely syncs with the original.

For that reason, Office 365 only accepts the PST file as an importable file type.

Then, how to import OST to Microsoft 365?

Don’t worry.

In this article, I will unveil the best method to upload any OST to Office 365 with only a few clicks.

Without wasting any more time, let’s begin.

Table of Content

Click the topic you find relevant to jump to important information.

How to Import OST Files into Office 365? Overview

As mentioned earlier, Office 365 is an outstanding online service; but it doesn’t import OST files. Microsoft 365 imports only PST (Personal Storage Table) files.

This condition requires us to convert the OST file into the PST format and then complete the import process.

So, after considering all angles, I can classify two methods to import OST files to Microsoft 365:

A manual approach:

Manually convert the OST file, and then use either Azure AzCopy or Drop Shipping to migrate the OST (now PST) to Office 365.

Use a third-party migrator tool to upload the OST to Office 365 directly.

Let’s see the detailed explanation of the methods mentioned above.

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Method-1: Import OST to Office 365 Manually

Before importing the OST file, let’s change it into an importable file format.

Step 1: Make OST File Importable to Office 365 Account

We will use the export function of Outlook in this case:

Follow these points:

  • Run Outlook on your PC
  • Then go to File> Open&Export> Import/Export
  • Afterward, hit the “Export to a file” option.
  • Then choose the “Outlook Data File (.pst)” option.
  • Subsequently, choose the data for conversion, and click on Include subfolders.
  • Afterward, Browse the save location.
  • Finally, click on Finish to convert the OST file.

Step 2: Use Azure Azcopy to Complete Import OST to Office 365

Know this before using Azure Azcopy to upload OST to Microsoft 365.

The Azure Azcpoy method is given separately by the Cloud platform and does not correspond to Office 365 directly.

Thus, we need to keep some prerequisites handy.

First, you need the Mailbox Import and Export Role from the Office 365 administrator. This Role is off by default.

The PST file size is limited to 20 GB max. So, we cannot upload large-sized PST files.
Single message size caps at 35 MB.

This method will work only with the AzCopy tool. Don’t bother using Azure Storage Explorer to upload the file.

Make sure that the PST file is in a network-shared folder.

After you’ve uploaded the file to Office 365, please update the retention hold policies. The old settings might cause the automatic deletion of data.

Now that the prerequisites are understood.

Let’s move on to the steps.

  • Install the Azure AzCopy and copy the SAS (Shared Access Signature) URL. The URL will give the required permissions.
  • Upload PST file generated using OST to Office 365
  • Afterward, create the PST mapping (CSV) file.
  • Then, create an import job in Office 365
  • Finally, filter the data and start the PST import job.

If you are not able to perform the above steps then move to step 2.1.

Step 2.1: Use Drive Shipping

Make good use of the Drive Shipping service of Microsoft to upload any OST to Microsoft 365.

In this service, we need to transfer the OST file to a hard drive and ship the disk to a Microsoft center.

Now, let’s move to the migrator tool method.

Method-2: Import OST to Office 365 via Migration Tool.

In the previous method, we experienced how complex and time-consuming it is to import OST to Office 365 through conventional means.

Not only that, we cannot use the previous method in cases like orphaned OST files, losing access to the Exchange/IMAP server, a corrupt OST file, and errors in the OST file.

Then, is there a better method?

A way to migrate OST to Office 365 in less time and in simple steps?


We can reduce the complexity and time requirement using an automated third-party tool.

One such tool is the 4n6 OST to Office 365 Migrator Tool.

The 4n6 software is the creation of multiple industry experts. Moreover, this OST to Microsoft migrator will address the current and future needs of Outlook users.

It is the one-stop solution to import OST files to Office 365 account directly.

Benefits of 4n6 Migration Tool:

  • Convert your OST into many different formats, and have flexible data sharing.
  • Data migration becomes quick, as we can easily convert and move any OST.
  • Intricately designed UI will help in better navigation.

Steps to Import Any OST to Office 365

All the listed steps are verified and safe to use for any size OST file.

ost to office 365

Step-1: Download OST to Office 365 backup tool and install it on your Windows OS.
Step-2: Run the tool and click on the Open drop down and click Choose File From a Folder option.
Step-3: Preview complete data into different preview modes and move to the next step.
Step-4: Afterward, click on Export, and under Email Services, choose Office 365 option from the list.
Step-5: Now, enter your Office 365 credentials and finally, hit the Save button and successfully upload OST to Office 365.

Benefits of Importing OST to Office 365

Migrating an OST to Microsoft 365 comes with its perks.

  • Better Accessibility: When we upload the OST to Office 365, we can use and access the file from anywhere and from multiple devices.
  • Secure Network: Microsoft 365 is one of the most secure spaces to keep data, and it also has data-redundancy techniques to safeguard our files from all danger.
  • Ease in data sharing: As the data is stored online, we can easily share the files.
  • Avoid unwanted interruptions: After we migrate OST to Office 365, we save ourselves from many interruptions.


In conclusion, Office 365 doesn’t import OST files but accepts PST format.

So, the only viable option left is this:

Import OST to Office 365 Manually or you can use OST to Microsoft 365 migrator tool.

However, as we observed, the manual approach is complex and time-consuming.
And it doesn’t work in situations like orphaned OST, etc.

Therefore, we need to employ a migrator tool like a 4n6 OST converter to import OST to Microsoft 365.