If you are using docomo carrier mail

1. Open the docomo Mail application, tap Other in the lower right corner, and then tap Mail Settings.
   

2. Tap docomo Mail Settings site in Mail Settings.
   

3. From the docomo Mail Settings site, tap the Receiving List setting.
   

4. Enter "tatsuno-system.co.jp" in the registration for incoming mail.
   

5. Tap Confirm at the bottom of the screen.
   

6. Tap Confirm Settings at the bottom of the screen.