What is embedding

 

Email is by definition plain text. When you send an email it is always transmitted in plain text, because the mail protocol can only receive and send text.

 

Here is a piece of html. It is also plain text. As opposed to binary data.

 

<TR><TD class=logotext style="padding-left: 5px"></TD>

<TD align=right style="padding-right: 5px; FONT-SIZE: 7pt; COLOR: #4e81c4; FONT-FAMILY: Verdana,Arial,fixed">

<a href="http://###URL###">Your Slogan here</a> </TD></TR>

 

So the internet consortium has invented methods for transmitting all kinds of non-text information through a plain text channel.

Basically the strategy is to convert it from some format to plain text for transmission, and then back again after reception.

 

That is the nature of MIME. (Multipurpose Internet Mail Extensions)

 

So when a document or image is transmitted it is actually being converted forth and back. If you open an email with images in it, and view the source code you will see something like this:

 

--0016369cff73d6b2da04679f4cfd

Content-Type: image/png; name=mapImg

Content-Disposition: attachment; filename=mapImg

Content-Transfer-Encoding: base64

Content-ID: <mapImg>

 

iVBORw0KGgoAAAANSUhEUgAAAfQAAAEsCAYAAAA1u0HIAACAAElEQVR42uy9

ebhl5XXeef/rxOnYJO52upN2IifupPM46WB3Ot1xumMcJ3Hix3HIk25bdiRr

QrMQoNloQmIeChACgcRYIKYqphKTEBQzCCiKqoIaoKqYQQI0IEXp5+m4u/31

fve9v6O3Ft/eZ+8z3HvOvd95nlXn1j7n7Hl/77fWete7Fl57eX+S3XTVOUmv

5/Y9nrbce3NiuUzLHrjj2nT7DRelnY/dn/70P//f9Xf/009+VC/XbzdedHJ6

 

Outlook does all that with out you think about it.

 

In the old versions like Outlook 2000, all such encoded items where detected as attachment.

But in newer versions, Outlook look at the "Content-Type" header to determine more precisely if it should show it as and attachment.

Here you can see that it is an image:

Content-Type: image/png; name=mapImg

 

So Outlook will not show it as an attachment because that is obstructing your logical view of what is attachment and what is not. It is a matter of interpretation.