How does ProtonMail treat authentication failures?

ProtonMail, focused on privacy and security, treats authentication failures with particular strictness. As a provider attracting security conscious users, ProtonMail applies rigorous checking of SPF, DKIM, and DMARC to protect users from spoofing and phishing.

Messages failing authentication face aggressive filtering or rejection. ProtonMail users expect verified sender identity as part of the security focused service they chose. Partial authentication or misalignment issues that might slide at consumer providers often trigger problems at ProtonMail.

Senders reaching ProtonMail users should ensure impeccable authentication configuration. Test specifically with ProtonMail accounts to verify all authentication passes correctly. Given ProtonMail's user base expectations, authentication problems damage trust more significantly than at mainstream providers.