This is Takeda from customer support team in KDDI.
Thank you very much for your report.
We got a huge complain from the customer about this trouble
that the customer could not receive the e-mail nearly 4 days.
We, KDDI, are very considering this trouble and strongly request to you
to inform us in advanced if you changes any settings on the server next time.
We hope you to understand and cooperate with us.