If you are migrating from a previous email or hosted exchange provider to Office 365, you have two options for how to proceed.
1. Start Fresh
Your new Office 365 service starts with an empty mailbox, calendar and contacts. If you prefer not to import your previous data, we recommend making an archive of your existing mail, should you need to refer to it at a later stage. For instructions on exporting your data, please see: https://neural.zendesk.com/hc/en-us/articles/200599565-Export-Outlook-items-to-an-Outlook-Data-File-pst-
Once you have configured Outlook to use Office 365, you can open this archive by choosing File > Open > Outlook Data File, then select the file you created above. This will add the archive to the folder list on the left.
2. Import your data to Office 365
If you would prefer to keep your emails, contacts and calendar details from your previous provider, you will need to export your data before re-configuring Outlook, then import it again once complete.
To export your data, please see the following article: https://neural.zendesk.com/hc/en-us/articles/200599565-Export-Outlook-items-to-an-Outlook-Data-File-pst-
Once you have reconfigured Outlook, please use the following to import your data to Office 365: https://neural.zendesk.com/hc/en-us/articles/200599575-Import-Outlook-items-from-a-Personal-Folders-file-pst-