Which email can be confirmed as internal?

Generally, it is a work mailbox dedicated to recruitment by human resources/personnel.

It is different from the email address such as QQ you usually use.

Generally, it is a suffix linked to your own enterprise, such as @ xxtech.com. For example, if an enterprise's domain name is www.abc.com, its post office landing address is mail.abc.com. According to the space of the post office, many users can be assigned, such as abc@abc.com, and this user is the internal mailbox of the enterprise.