Skrzynka pocztowa z listem and other 80,800 icons from Icons8 icon pack follow the visual guidelines of the operating systems: Windows, iOS, Android KitKat, and Material. PNG format is free up to 100x100 px. Icons are availble for download in PNG and vector (SVG, PDF, EPS, and more).
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.