There is an image of the back of a mailing envelope. Over the bottom right hand corner of the image there is a circled check mark that seems to be indicating that an action has been completed involving the envelope.
This Received icon is made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 5,500 icons, all in the same style and quality.