Article ID: 2762067 - View products that this article applies to.
Not sure what release of Office 365 you're using? Go to the following Microsoft website:
Am I using Office 365 after the service upgrade?
A user's mailbox in Microsoft Office 365 pre-upgrade no longer exists, and the user can no longer access email messages in Office 365 pre-upgrade.
This issue occurs if the user no longer has an Office 365 pre-upgrade license. For example, this occurs if the user's Office 365 pre-upgrade license was removed.
To resolve this issue, reassign an Office 365 pre-upgrade license to the user. For more information about how to do this, go to one of the following Microsoft websites:
Still need help? Go to the Office 365 Community
Article ID: 2762067 - Last Review: June 19, 2013 - Revision: 6.0