Proton Mail automatically saves all email addresses you have sent a message to in your Proton Contacts, along with the default display names associated with the addresses.
The Automatically save contacts feature is enabled by default. To disable this feature (or switch it on again if previously disabled):
1. In the Proton Mail web app, click the Contacts icon in the side panel at the top right of your inbox.
2. Click the Contacts dropdown menu, and select Settings.
3. Turn the Automatically save contacts switch on or off to enable or disable this feature.