What it means
From everyone automatically adds direct invitations from any sender to the calendar. Only if the sender is known limits automatic additions to contacts, members of your organization or people with whom you previously interacted. When I respond to the invitation in email waits for your response before adding it. Google says these changes apply to new invitations. A malicious known contact or compromised coworker account can still slip through a known-sender rule.
A real-world example
A fake technical-support event arrives from a stranger. With From everyone, it may occupy tomorrow's grid. With the known-sender option, the user instead sees an invitation email and can inspect it before responding. A legitimate dentist's first invite may also wait.
What to do
Open Calendar Settings, Event settings, and select the rule that matches your tolerance for unsolicited entries. Test with a controlled unknown account. Report a malicious event as spam and check whether other people can see pending invitations on a shared calendar.
The distinction that matters
An invitation email is not an accepted event. Adding someone to Contacts to make their events appear also changes how future invitations from them are handled, so do it only for a trusted sender. Calendar's known-sender label is a relationship signal, not security verification. A work administrator may constrain the menu. Review the invitation's links and organizer through a separate trusted channel when it requests payment or account access. The rule helps control your calendar view but cannot replace judgment about the content.
Google Calendar invitation settings
