Nothing in your mail filter, because the call never touches it. In Mandiant’s M-Trends 2026, voice phishing reached 11% of confirmed initial infection vectors and passed email phishing, which fell to 6%. The usual goal is to talk someone into approving a remote support session, which hands over more than a stolen password would.
What works is an expectation set well before the call. Every email we send states that we will never ask for passwords, payment details or remote access by email, and gives you a number to verify against. We set the same thing up on your outgoing mail, applied centrally so it is on every mailbox without anyone having to remember.
It does not replace multi-factor authentication, and it does not replace verifying callers on your own help desk. It costs nothing and it works at the one moment when no technical control is present.