Envelope recipient
An address given in an SMTP RCPT TO command: where the message is actually delivered, whatever its To and Cc headers say.
What it means
RFC 5321 calls it the forward-path. A message has one envelope recipient per RCPT TO, and those addresses alone decide delivery. They can differ from the visible recipients for ordinary reasons: Bcc recipients appear only in the envelope, a forwarding rule replaces the original address with a new one, and a mailing list delivers to each subscriber while the To header still names the list.
Once the message is stored, the envelope recipient is visible only if the receiving system recorded it, usually in a Delivered-To header or in the for clause of a Received header. RFC 5321 allows only one address in that clause, since listing every recipient would expose the Bcc addresses.
Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5321, section 2.3.1: Mail Objectsrfc-editor.org
- RFC 5321, section 4.4: Trace Informationrfc-editor.org
- RFC 9228: Delivered-To Email Header Fieldrfc-editor.org
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