ProtonMail now blocks tracking pixels and hides your IP address, the company announced on Wednesday. The web app is mentioned so these features may not be present in the mobile apps.
By default, ProtonMail on the web now protects your privacy by: Blocking tracking pixels commonly found in newsletters and promotional emails, preventing senders from spying on your mail. Hiding your IP address from third parties so your location remains private.
Update: A ProtonMail spokesperson confirmed that this is indeed only for the web app, and expanding it to the mobile apps is part of development plans.