You may get an error message when accessing Office 365 mailbox for the first time. Error message appears like below
Something went wrong
A mailbox couldn’t be found for Rajkumar@domain.com.
Date:2/10/2020 6:10:48 AM
Issue could be because of the Office 365 license not assigned. If you see the license assigned, reprocess the license once and the issue will be resolved.
Once the license reprocessed, you will have access to the mailbox.