Down Arrow Envelope.
The back of envelope with a down arrow on top. Generally depicted in white (except for Google’s yellow design) with a red or blue arrow.
Commonly used an icon before an email address. May also represent downloading, direct messages, or mail (post) more generally. Its original intent may have been to indicate sealing and delivering a letter in an envelope.
Microsoft’s design previously resembled an incoming envelope. Early designs from Apple featured a right arrow with the envelope oriented lengthwise. SoftBank originally animated a rightward-moving arrow and envelope, suggesting sending or sent.
Envelope with Arrow was approved as part of Unicode 6.0 in 2010 under the name “Envelope with Downwards Arrow Above” and added to Emoji 1.0 in 2015.