Email forwarding
Automatically sending mail received at one address on to another, which changes the path a message takes and often breaks SPF, while DKIM usually survives.
What it means
Forwarding replaces the envelope recipient and sends the message on from the forwarding server. If the forwarder keeps the original envelope sender, the final receiver sees mail for the original domain arriving from the forwarder's IP, which that domain's SPF record does not list, so SPF fails. DKIM survives as long as nothing in the signed header or body changes. Google's advice to forwarders is to change the envelope sender to the forwarding domain, avoid modifying the subject, body or MIME boundaries so DKIM still passes, and add a header showing the message was forwarded.
Forwarding is also a security control: Exchange Online can block automatic forwarding to outside addresses through its outbound spam policy, returning an NDR to the sender. RFC 7960 describes these forwarding problems for DMARC and the mitigations in use.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- Google, Gmail Help: Best practices for forwarding email to Gmailsupport.google.com
- RFC 5321, section 3.4: Forwarding for Address Correction or Updatingrfc-editor.org
- RFC 7960, section 3.2.2: ReSendersrfc-editor.org
- Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes