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The bat header format

The Bat! v3

Date: Fri, 7 Feb 2025 15:23:52 +0300
From: Username <username@sendinghost.com>
Message-ID: <1066947962.20250207152352@gmail.com>
To: Username <username@receivinghost.com>
Subject: header test. the bat
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Type: multipart/mixed; boundary="----------069134143049E2085"

Message-ID format:

Message-ID consists of 4 parts

  • A random string of numbers
  • A timestamp of the format YYYYmmDDHHMMSS
  • The @ symbol
  • The domain of the sending host

As at March 2025, there is an interesting nuance in Message-ID when used with the mail agent's Postponed Sending feature. When a mail's sending is postponed, the Date header will be updated accordingly, but the timestamp within the Message ID will not.

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