Spoofed e-mail is an e-mail that is sent by a malicious company or other person under the guise of someone else, using the e-mail mechanism that allows you to freely set the sender's address and name.
It is well known that people are cautioned against spam emails claiming to be from Japan Post or other major companies.
These have become an international problem, and the reality is that it is impossible to prevent the act of sending spam mail itself, but it is possible for recipients to set their settings so that they do not receive it.
Each mobile phone company has a setting menu such as "anti-spoofing" and "spoofing regulations".
Below is the settings page for a major mobile company.
●NTT docomo
https://www.nttdocomo.co.jp/info/spam_mail/spmode/domain/
●au
https://www.au.com/support/service/mobile/trouble/mail/email/filter/detail/forgery/
●SoftBank
https://www.softbank.jp/mobile/support/antispam/settings/antispoof/
These filters should be enabled by default, but depending on your device's contract period and contract details, the settings may be disabled, so be sure to check.
(If using a PC, please check the settings of your provider and email software.)
This setting allows you to block unauthorized emails that do not have legitimate sending domain authentication.