Situation :
The domain user account has been deleted, but Azure account still remain active (not deleted)
Due to the account doesn't exist, the user could not access the domain but exchange online still active.
Resolution :
log into the local server (DC preferred). Create the user with same credential and changeable password including the right group.
Note :
If the account is delete from the Azure, the email included all content will be gone with no grace period.
One drive still be alive for 30 days