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Thunderbird header format

Mozilla Thunderbird version 1.0 running on Microsoft Windows generates headers in the following format:

Message-ID: <>
Date: Tue, 07 Dec 2004 13:42:09 -0500
From: User Name <>
User-Agent: Mozilla Thunderbird 1.0 (Windows/20041206)
X-Accept-Language: en-us, en
MIME-Version: 1.0
Subject: Testing
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Extensions such as enigmail may add extra headers.

The Message-ID field has three parts:

  1. The time the message was sent in seconds past the epoch in hexadecimal.
  2. A random value called a salt. The salt is of the format #0#0#0# where # is a random digit. Because Thunderbird treats the salt like a number, it may be shorter if the leading digits are zeros. For example, a salt of "0030509" would display as "30509".
  3. The fully qualified domain name of the sender.
Message-ID: [time].[salt]@[domain-name]


Information on the Message-ID header was derived from the source code, specifically the function msg_generate_message_id in mozilla/mailnews/compose/src/nsMsgCompUtils.cpp.