Does Proton block suspicious emails without making it reach the inbox?
I know there is a section for potential spam mails. But I wonder whether Proton block some of them so that they won't even reach that section. I am using it as my primary email right now and recently a recruiter tried sending me an email for tech discussion but it never reached my inbox. They were sure it was sent, and I later received it on my alternate email (gmail). Is there any possibility that this could have happened for other reasons?
If the recruiter sent an email from a domain that wasn't properly configured (DKIM+SPF, etc) then it would have sent a bounce email, which may have gone to the recruiter's span folder, or they may have ignored the bounce email thinking it was a phishing email.
It depends. They, like all mail services, will follow DKIM and SPF so if someone has DKIM+SPF set on company.com correctly and someone sets up a newsletter sending from mail.company.com, that's a misconfiguration that causes Proton, Gmail, Yahoo, AOL, Microsoft, Apple, and all the other large players to bounce the email.