The cause is due to the receiving side's settings or communication conditions. Please refer to "Precautions for registering your e-mail address" and make sure that your e-mail address is set up to receive messages reliably. In particular, please avoid using carrier e-mail addresses, as they often cause problems. If you wish to change your e-mail address to another address, please contact us using the form below and provide us with the e-mail address before and after the change.