All public facing aspects of the system can be branded (i.e. emails to signers and your signing page). This article is about branding your emails only. You need to be an admin user.
Go to 'Admin' > 'Signer experience'. At the top of that page add your logo and change the format of your outbound emails.
To change the email logo, go to the email preview (which is the first section ) and below that you will see a button labelled 'Add/remove email logo'. Or drag and drop your logo image right onto the preview email.
Here's a video that shows the email editor in action:
