Site logo shows in Webmail client but doesn't show in Gmail

Problem/Motivation

Since launch of Drupal CMS and I have used this module in all my new sites, I have never seen the site logo displayed in emails in Gmail but the logo displays in my host's Webmail client.

Email header in Gmail:

Email header in Roundcube:

Steps to reproduce

• Set up a Drupal CMS website.
• Set email notification in webform.
• Submit the form.
• Observe email notification in Gmail and observe on the host provider's email client.