How do I add an avatar/logo to my emails?
By default, that image people see next to your email in their inbox will be the first character of your company's name. Alternatively, it may look like this:
Occasionally we get asked how to add a logo so that it will appear next to your email messages in the end-user's inbox instead. Unfortunately, this is not something you (or we) control exclusively as part of the email sending process but rather it is determined by the recipient's inbox provider or email client.
Avatars shown in Gmail
When sending from G-Suite, Gmail will use the sender's profile image as you would expect. When sending from non-Gmail sources, you used to be able to signal which image to use by uploading it to a Google+ account but those days are long gone. These days, Gmail will use your BIMI configuration to determine which image to show.
BIMI stands for "Brand Indicators for Message Identification." It is an emerging email specification that enables the use of brand-controlled logos within supporting email clients. You can read more about what BIMI is and why you should care in this article by Litmus as well as in this BIMI Q&A article from Email on Acid.
Avatars for other email clients
BIMI is also used by Yahoo! and we believe more inbox providers are sure to follow but many other email clients (Thunderbird, Airmail, and Postbox, for example) use Gravatar to display the sender image. To take full control of this avatar in the email clients that support it, create a Gravatar account, verify your email address, and choose your desired image.
Gravatar is also used by Customer.io to automatically show images for the People you add to your account.