This is a common inbox on the roadside. It should be noted that the blue or gray mailboxes displayed on most system platforms have the red mark facing upwards and there are mails in the slot. For example, the receiving envelope displayed by the Google system is in an open state. There is a yellow envelope in the inbox. In addition, the emoticon can be used not only to express the meaning of e-mail, postal delivery, but also to mean that there is a new letter, and it can also mean that the mail has been delivered.
