How do I get an icon in Google Inbox?
<p>I receive e-mails from various senders, and when I view them in Google Inbox, either on inbox.google.com, or on the Android App, some have an icon in a circle next to them... others just have a letter.</p>

<p>BitBucket, for example, has a nice icon when they send me an e-mail:
<a href="https://i.stack.imgur.com/44EoV.png" rel="noreferrer"><img src="https://i.stack.imgur.com/44EoV.png" alt="BitBucket icon"></a></p>

<p>The question:</p>

<p>Does Google Inbox fetch this picture with some kind of G+ magic, or are certain e-mail headers involved here?</p>

<p>How do I implement this in my own solutions when sending out e-mails?</p>