Open Mailbox With Lowered Flag on Facebook

What it signals here

reaction meaning

Less commonly used as a reaction; sometimes placed in comments to express that someone hasn't received an expected update.

comment use

Posted on event pages or group posts to ask if there are any updates or to note that no response has come.

boomer interpretation

Likely interpreted literally — indicating that a physical or email mailbox is empty or has been checked already.

group use

Used in neighborhood groups or community pages to indicate that no new community notices or letters have arrived.

See it elsewhere