Updated November 2023

Gmail/Google Workspace: Shown in both the mobile app and webmail when you open the email. Additionally, the logo is visible in the inbox list on the webmail.
Apple: Shown in the mobile app only once you open the email.
Fastmail: Shown in the mobile app and webmail only when you open the email.
La Poste: Shown in webmail only.
Yahoo: Shown in the mobile app and webmail when you open the email. Additionally, the logo is visible in the inbox list on the webmail.
Zone: Shown in webmail only.

Expected 2024:

Microsoft Outlook