X-Message-Delivery in Hotmail Messages

Question

Recently I stared deciphering the hotmail inbox/junk folder placement. After long searching I found out that Hotmail/Outlook is using their X-Message-Delivery tag they input in each mail, to determine alot of things. If you go to source of an e-mail you can see an X-Message-Delivery similar to this :

Vj0xLjE7dXM9MDtsPTE7YT0wO0Q9MjtHRD0yO1NDTD00

which if you BASE64-Decode it you get

V=1.1;us=0;l=1;a=0;D=2;GD=2;SCL=4

Based upon my research, I found out that following things are causing a message to go to the junk folder,

If "D=x" is higher then 1
If "GD=x" is higher then 1
If "SCL=x" is higher then 0

Other then that I found out that V=1.1 is allways the same and does not change in any e-mail I received (or atleast the ones I checked)

I think that "a=x" is meaning if the sender is in the receivers adressbook, or is atleast known by the receiver. If its 0 its a new sender, and therefor more likely to go to the junk folder, if its a=1 it helps to get into inbox.

I think the l=1 or l=0 has something to with, if images are blocked or not for this sender upon an open. Although I did not find this very consistent.

Does any of you know, what these tags stand for?

D=
GD=
us= 

If you do, do you also know what they would change from 0 to 1 or 2 ?

Thank u!

Answer 1

mime-version

SCL refers to Spam Confidence Level (SCL)

SCL ratings of 2, 3, 4, 7, and 8 are not used by the service. An SCL rating of 5 or 6 is considered suspected spam, which is less certain to be spam than an SCL rating of 9, which is considered certain spam. Different actions for spam and high confidence spam can be configured via your content filter policies in the Exchange admin center. For more information, see Configure Content Filter Policies. You can also set the SCL rating for messages that match specific conditions by using Transport rules, as described in Create a transport rule to identify mail as spam or not spam by setting the spam confidence level (SCL).

http://technet.microsoft.com/en-us/library/dn798345(v=exchg.150).aspx

http://technet.microsoft.com/en-us/library/jj200686(v=exchg.150).aspx

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GD.. after an exhaustive search.. I believe that it refers to the GD2, the graphics library associated with PHP but I have no references to substantiate that. Or, I found an obscure mention of a term referred to as 'guarantee delivery' but it was a very subtle mention and I could not found any further reference to it. However, it does make sense possibly..

Email senders that have given Hotmail a reach around and gotten special treatment as being flagged 'not spam no matter what.. guarantee delivery'. Seems reasonable..

The only reference I could find in any RFCs for GD was RFC6035 Which defines GD as GapDuration

"GD" EQUAL (1*7DIGIT) ;0-3,600,000 -- milliseconds
BLD=0 BD=0 GLD=2.0 GD=500 GMIN=16

GDuration gd = (GDuration) table.get(context);

http://media.proquest.com/media/pq/classic/doc/1397920421/fmt/ai/rep/NPDF?_s=PRwJ1WMP1Dw7%2F7ZDFW5hXUNyfPo%3D

but I don't really think they're related.

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I doubt that it means Generate-Delivery-Report as Manuel guessed. Reason being, Generate-Delivery-Report is already a defined header field so it's not necessary to create another field.

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The X- headers are defined originally in RFC822 Section 4

By the time I gave up on my search of GD I quit.

Whatever they mean, I'm betting that whatever they may have meant has been forgotten so long ago that probably no body at Hotmail even knows what it means anymore and even more unlikely that there will be any actionable methods for you to change whatever they are. I'm kinda still in shock that I couldn't find ANYTHING.. I'm usually really awesome at researching and digging up obscure data. ;p

Further Resources:

• RFC2076 : Common Internet Message Headers
• RFC2045 : Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies
• RFC4021 : Registration of Mail and MIME Header Fields
• BCP178