Indirect mail flows and DMARC

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DMARC is an anti-phishing technology. It has recently been repurposed by large mail providers for public webmail domains.

DMARC alignment requires that the From: line address in a mail message match either a DKIM signature d= domain, or an SPF-validated bounce address domain. Depending on a domain's published policy, unaligned mail may be quarantined, i.e., relegated to the spam folder, or rejected with a 5xx SMTP code by recipient systems. A variety of long standing mail practices often create unaligned mail.

Forwarding

  • discussion mailing lists
  • annotating forwarders
  • annotating anti-virus

Third party origination

  • Newspaper mail-an-article
  • Small clients at ESPs
  • Notifications from devices