Attachment: EML file with HTML attachment (unsolicited)

type.inbound

// has EML attachment
and any(attachments,
        (.file_extension == "eml" or .content_type == "message/rfc822")
        and any(file.parse_eml(.).attachments,
                // HTML file inside EML attachment
                // we've seen files named ".htm.", which results in an empty
                // .file_extension, so instead we look at .file_name
                // they should be rare enough in EML attachments to not cause
                // extraneous FPs
                strings.ilike(.file_name, "*htm*")
                or .file_type == "html"
                or any(file.explode(.), .flavors.mime == "text/html")
        )
)

// exclude bounce backs & read receipts
and not strings.like(sender.email.local_part,
                     "*postmaster*",
                     "*mailer-daemon*",
                     "*administrator*"
)
and not regex.icontains(subject.subject, "^(undeliverable
| read:)")
and not any(attachments, .content_type == "message/delivery-status")
// if the "References" is in the body of the message, it's probably a bounce
and not any(headers.references, strings.contains(body.html.display_text, .))
// unsolicited or fails authentation
and (
  (
    profile.by_sender_email().prevalence in ("new", "outlier")
    and not profile.by_sender_email().solicited
  )
  or (
    profile.by_sender_email().any_messages_malicious_or_spam
    and not profile.by_sender_email().any_messages_benign
  )
  or (
    sender.email.domain.domain in $org_domains
    and not coalesce(headers.auth_summary.dmarc.pass, false)
  )
)

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