Microsoft now have a fairly straightforward way to import large Outlook PST files into Office 365. Using this process to upload large amounts of email should be considerably quicker, and more reliable, than pushing the email up to Office 365 with Outlook, or your mail client of choice.

For the most recent upload I performed, the upload to Azure storage maxed out the 40 Mb/s upload on my internet connection. I’ll have to run the next one from somewhere with 1000 Mbs Fibre and see how it goes.

While this process uses Azure storage to hold the PST for import, you don’t need a separate paid Azure storage account – it is covered under your Office 365 account.

Microsoft have a comprehensive step-by-step guide on how to upload the PST and then import it to Office 365.

Use network upload to import your organization’s PST files to Microsoft 365

First you need to be a Global Admin, and go into the Exchange Admin Centre and assign yourself the Mailbox Import Export role, under Permissions > admin roles.

Then log in at https://protection.office.com/ and go to Information governance > Import > Import PST Files.

Click on the +New Import Job button to create a new import batch. If you don’t see the button, make sire you have given yourself the Mailbox Import Export role. Sometimes this role takes a bit of time to take effect. Microsoft say it can take up to 24 hours, but it’s never been that long in my experience. Last time I did this, it took 30-45 minutes before I could create a new import job.

After clicking on the new import job button, name your job. No capital letters, or spaces. Then select the option to upload your data.

If you follow the link to download AzCopy, you’ll get the msi for an older version. Instead search for AzCopy via your favourite search engine. At the time I wrote this v10 was the latest version.

https://docs.microsoft.com/en-us/azure/storage/common/storage-use-azcopy-v10

In later versions, there’s also Linux and macOS flavours, as well as 32 and 64-bit Windows. Unfortunately however the macOS version wasn’t signed, so my Catalina system didn’t want to open it. I had to find the binary in the Finder and right-click on it to open it, at which point I could then confirm that the signature couldn’t be verified and tell macOS that I wanted to open it anyway.

Back to the Security and Compliance centre, click on the link to show the network upload SAS URL. This is the url to which you’ll upload the data to Microsoft.

You’ll also need to make a mapping file, which is a csv that tells Office 365 what data goes where.

Here’s how to create the PST Import Mapping file.

Then, import the data with AzCopy. Use the syntax:

First, get the authentication token:

azcopy login

Then, copy the pst to Azure

azcopy cp /path/to/outlook.pst "long SAS URL"

Make sure you enclose the SAS URL in quotes so that the shell doesn’t interpret the characters in it as shell commands.

Once it’s finished uploading, then you can continue with the import tin the Security and Compliance centre.