Impersonation using recipient domain (untrusted sender)

type.inbound

// only 1 To: recipient
and length(recipients.to) + length(recipients.bcc) + length(recipients.cc) == 1
and any(recipients.to,
        // custom domains only
        sender.email.domain.domain not in $free_email_providers

        // recipient's domain is in the sender's display name
        and strings.icontains(sender.display_name, .email.domain.root_domain)
)
and not (
  (
    strings.contains(sender.display_name, "on behalf of")
    and sender.email.domain.root_domain == "microsoftonline.com"
  )
  or (
    strings.contains(sender.display_name, "via TransferXL")
    and sender.email.domain.root_domain == "transferxl.com"
  )
)
and all(recipients.to,
        .email.domain.root_domain != sender.email.domain.root_domain
)
and (
  profile.by_sender().prevalence in ("new", "outlier")
  or (
    profile.by_sender().any_messages_malicious_or_spam
    and not profile.by_sender().any_messages_benign
  )
)

// negate highly trusted sender domains unless they fail DMARC authentication
and (
  (
    sender.email.domain.root_domain in $high_trust_sender_root_domains
    and not headers.auth_summary.dmarc.pass
  )
  or sender.email.domain.root_domain not in $high_trust_sender_root_domains
)