Date header
The required header field recording when the author's program finished the message and released it for sending, with a numeric time zone offset.
What it means
RFC 5322 calls it the origination date: the date and time the creator of the message indicated it was complete and ready to enter the mail system, for example when the author clicked Send. It is one of only two required fields, with From, and appears once. The format is fixed, as in Date: Tue, 20 Oct 2026 09:15:00 +0200.
The Date is written by the sender's software and nobody verifies it, so it can be wrong; Received headers record when servers actually handled the message. A submission server may add a missing Date or correct a malformed one (RFC 6409), and Yahoo lists a date outside an acceptable range among its policy rejections.
Example
Date: Tue, 20 Oct 2026 09:15:00 +0200Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5322, section 3.6.1: The Origination Date Fieldrfc-editor.org
- RFC 6409, section 8.2: Add 'Date'rfc-editor.org
- Yahoo Sender Hub: SMTP error codessenders.yahooinc.com
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