Function authenticated 

pub fn authenticated(
    results: Option<&AuthResults>,
    headers: &RawHeaders,
    sealers: &[String],
) -> bool

Whether a message is authenticated, as the results its account trusts record it (read_auth_results: Sioul’s own stamp, else your provider’s). It is not when SPF and DKIM both failed, unless DMARC passed, or ARC passed on a chain whose newest seal is a sealer’s you trust (sealers: your provider’s, your own domains’; arc_sealer): forwarding breaks SPF, and a forwarder that changes the message breaks DKIM, but anyone can seal a chain of their own. “none” (nothing published to check) is no failure, nor is a softfail; no results at all say nothing. DMARC failing under a policy is forged (judge_sender), set aside before this is asked. Mail that is not authenticated is not taken as coming from the address it shows (porch.rs: its sender is a stranger).