Yes, as per @mfranz , if the email address imported does not match an existing user it will create a new user.
The following tip is given in the FNMSInvAdaptersAndConnectorsReference.pdf:
Tip: There are frequently differences between a user's corporate email address (such as Sam.Doe@tmnis.com)
and the same user's email address registered in Microsoft Office 365 (such as
Sam.Doe@tmnisoffice365portal.com). Since only the email addresses are available for matching (given that
your Active Directory accounts are not reflected in the Microsoft Office 365 online service), this can lead to duplicated user records. To avoid duplicate records, you can, prior to importing from Microsoft Office 365 Online Service, populate your existing user records with the Microsoft Office 365 email address in the Alternate email field. You may want to consider using a Business Adapter to make widespread updates. If you have not done this prior to importing from the Microsoft Office 365 (and as a result some user records are now duplicated), you can update the Alternate email field in your AD-based records at any time, and the next full import and compliance calculation automatically cleans up those duplicates.
