If you access KUMOI just after you have activated your ECS-ID, the error "X-OWA-Error: Microsoft.Exchange.Data.Storage.UserHasNoMailboxException" or others occur, and you cannnot use KUMOI.

KUMOI becomes available in the next day of your activation, and you should try again in the afternoon of the next day of your activation. Please contact to the support desk if you cannot log in although you have already activated two or more days before.