The image is of a mailbox with the door opened. The flag is up on the right side of the box. Part of an envelop is showing inside the box. The back of the envelop is showing the seam where the envelop was sealed.
This is a Postal icon. We've made it in iOS style
, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 13,300 icons, all in the same style and quality.