Why does Zendesk display the Zendesk logo as the sender’s avatar for some email clients?
This behavior happens when you use Zendesk native email addresses to send email notifications to your clients. If you use an email that looks like firstname.lastname@example.org, the mail client of your customers may render the Zendesk logo as the avatar of the sender.
To change this behavior, add your own external address to your account. For more information, see this article: Adding support email addresses for users to submit tickets.
Find below two examples of how avatars look when an account sends notifications through an external address and a native support address.