In the USA, an open mailbox with the lowered flag denotes that no mail has been delivered and that there is no mail inside the box to be picked up by the postman. Can be used when you have nothing to say or no opinion about a matter.
The open mailbox with lowered flag emoji was introduced in 2010 and released as part of the Unicode 11.0 standard. This emoji can be found under the objects
category. Because the open mailbox with lowered flag emoji has been around for quite some time, it should display correctly in the majority of operating systems.