Export or backup email, contacts, and calendar to an Outlook .pst file
Microsoft's instructions on exporting email can be found here.
When an Outlook app - such as Outlook 2016 - is installed on your computer, you can use it to move email, contacts, and calendar items from one email account to another.
For example, let's say you have an Office 365 mailbox and a Gmail account. You can add both of them to Outlook 2016. Then, you can use Outlook 2016 to export items from your Gmail account and import them to your Office 365 mailbox.
You export items by creating a .pst file, which is an Outlook Data File that contains your messages and other Outlook items and is saved on your computer. To learn how to import items after you export them, see Import email, contacts, and calendar from an Outlook .pst file.
How to export email, contacts, and calendar items from Outlook to a .pst file
Choose from the following list of export instructions.
You can add your Office 365 email account to an Outlook app, such as Outlook 2016 or 2013. Then, you can use Outlook to move email, contacts, and calendar items into your Office 365 mailbox. Here's what you do:
Add your Office 365 email account to Outlook. After you do this, Outlook will automatically sync with Office 365. You'll see the contents of your Office 365 mailbox appear in Outlook.
Choose from the export instructions to export your email from your source account to a .pst file.
For example, if you have Outlook 2010, choose "Outlook 2010: Export Outlook items to a .pst file".
Choose from the export instructions (below) in this article to export your email to a .pst file.
For example, if you have Outlook 2016, choose "Outlook 2013 and Outlook 2016: Export Outlook items from a .pst file".
After your email data is exported to a .pst file, it's portable! You can import it to other email accounts. If you want to do this using Outlook, see Import email, contacts, and calendar from an Outlook .pst file.