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Could somebody please explain the logic of Message-ID created by MS Outlook? especially this part “D45A2C0A.EB29”

User-Agent: Microsoft-MacOutlook/14.6.9.160926
Date: Tue, 22 Nov 2016 17:08:26 -0600
Subject: Video playback error
From: “AAAAAAAAAAAA AAAAA, BBBBB (BBBBB AAAAAA)”
 <bbbbb.aaaaa@my.domain.com>
To: “ZZZ, YYYY P (YYYY ZZZZ)” <yyyy.zzz@my.domain.com>
Message-ID: <D45A2C0A.EB29%bbbbb.aaaaa@my.domain.com>
Thread-Topic: Video playback error
MIME-Version: 1.0
Content-type: multipart/mixed;
    boundary="B_3563051944_9433913"

RFC2392 confirms that 'both message-id and content-id are required to be globally unique. 'My question is specific for MS Outlook. I would like to know, what kind of logic used by MS Outlook to create the unique number? Can I extract time/date from that Hexadecimal number?

Vinod Kd
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1 Answers1

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According to RFC2822 - Internet Message Format, the Message ID should be unique for each instance of the message. It's considered optional and how the MESSAGE-ID field is created is up to the server:

The "Message-ID:" field provides a unique message identifier that refers to a particular version of a particular message. The uniqueness of the message identifier is guaranteed by the host that generates it (see below). This message identifier is intended to be machine readable and not necessarily meaningful to humans. A message identifier pertains to exactly one instantiation of a particular message; subsequent revisions to the message each receive new message identifiers.

Note: There are many instances when messages are "changed", but those changes do not constitute a new instantiation of that message, and therefore the message would not get a new message identifier. For example, when messages are introduced into the transport system, they are often prepended with additional header fields such as trace fields (described in section 3.6.7) and resent fields (described in section 3.6.6). The addition of such header fields does not change the identity of the message and therefore the original "Message-ID:" field is retained. In all cases, it is the meaning that the sender of the message wishes to convey (i.e., whether this is the same message or a different message) that determines whether or not the "Message-ID:" field changes, not any particular syntactic difference that appears (or does not appear) in the message.

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Eugene Astafiev
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    Thank you for answering my question. RFC2392 confirms that 'both message-id and content-id are required to be globally unique.' My question is specific for MS Outlook. I would like to know, what kind of logic used by MS Outlook to create the unique number? Can I extract time/date from that Hexadecimal number? – Vinod Kd Nov 27 '16 at 17:40
  • I suppose it depends on the transport provider, not Outlook. – Eugene Astafiev Nov 28 '16 at 14:30