Exactly, and even in the case when the emails are coming from a non-Proton service, the incoming emails are encrypted immediately after being checked for spam,

Exactly, and even in the case when the emails are coming from a non-Proton service, the incoming emails are encrypted immediately after being checked for spam, phishing or malware: https://proton.me/support/proton-mail-encryption-explained https://proton.me/support/proton-mail-encryption-explained.