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Re: [ietf-smtp] Proper definition of the term "email payload".

2019-03-31 21:46:47
Hi, I hope you (and they!) don’t mind me CCing two other people who have worked 
extensively on Python’s email library, and in fact much more than myself in the 
recent years.  RDM has done the bulk of the work on the new-in-Python-3 APIs, 
and Mark is a long time core developer on GNU Mailman (the project that spawned 
Python’s email library).

There are two ways I think about this, and I’ll use the original RFC numbers to 
clarify.  There’s RFC 821, which describes the on-the-wire protocol for SMTP 
transfers, embodied in Python’s smtplib library.  Then there’s RFC 822, which 
describes the format of the content of that SMTP transfer, but not the protocol 
itself.  Of course there are lots of developments along the way, but that’s 
unimportant for the way I think about these things.

What I think you are describing, where the headers are part of the payload, is 
more akin to RFC 821.  That’s the payload as far as the actual 
bytes-on-the-wire are concerned.  Python’s email library is for RFC 822 (and 
the many, many elaborations thereof), so in that case, the payload is the body 
of the message.  On more practical terms, the implementation makes this clear, 
and the APIs you use to change headers are different in form and function than 
the ones you use to change the body of the message.

I think the Python documentation is fairly clear about this distinction.  At 
least, I don’t remember seeing any feedback to the contrary, although RDM may 
have a better sense of that.  Of course, we are always open to improvements in 
Python’s documentation.


On Mar 31, 2019, at 10:57, Viruthagiri Thirumavalavan 
<giri(_at_)dombox(_dot_)org> wrote:

Hello IETF,

I need some clarification about the term "email payload".

Wikipedia says

In computing and telecommunications, the payload is the part of transmitted 
data that is the actual intended message. Headers and metadata are sent only 
to enable payload delivery

Python email library documentation says this.

An email message consists of headers and a payload (which is also referred to 
as the content). Headers are RFC 5322 or RFC 6532 style field names and 
values, where the field name and value are separated by a colon. The colon is 
not part of either the field name or the field value. The payload may be a 
simple text message, or a binary object, or a structured sequence of 
sub-messages each with their own set of headers and their own payload. The 
latter type of payload is indicated by the message having a MIME type such as 
multipart/* or message/rfc822.

It looks like Python email library author "Barry Warsaw" followed similar 
definition found in wikipedia when defining his library functions. But I feel 
like calling ONLY the email "Body Part" as "payload" is wrong. The term 
"payload" should refer to the entire "Message Part" in Email. i.e. Both 
Headers and Body.

When you place an order for a "box of beer", you are not paying only for the 
"beer cans", but also paying for the "container box". So the payload here is 
the entire box.

HTTP Example:

HTTP/1.1 200 OK
Date: Sun, 10 Oct 2010 23:26:07 GMT
Content-Type: text/html
Content-Length: 1234


<title>Hello World!</title>

(more contents)

If you take a closer look at this HTTP example, the headers are only just 
instructions for the client. The end user doesn't need to worry about any 
piece of information found in those headers. So wikipedia definition 
perfectly suited for applications like HTTP.

But in Email, When a mail get transferred from Hop A to Hop C via Hop B, the 
user in Hop A actually wants to deliver the whole "message part" to Hop C. If 
Hop B, strips the headers and transfer only the "Body" part, then it becomes 
an "Anonymous" message. So the end user requires the information found in the 
"Headers" too. e.g. From, Subject, Date etc. [In HTTP, title tag is 
equivalent to Subject and it's found in the "head" Markup, not in the HTTP 

As you can see, the user is interested in the "entire message". So the term 
"actual intended message" should refer to the "whole message" extracted from 
the DATA command. The "actual intended message" should be pictured like this 
in email.

Also note that, when you migrate your mails to another mail service, you need 
the whole message with Headers, not just the body.

Based on my points, I believe calling only the "Body" part as "Payload" is 
wrong. I would love to hear your thoughts on this. If Barry Warsaw is here, 
would love to know your opinion too.

PS: I did actually ask this question 2 years back in a stackexchange website. 
I wasn't satisfied with the answer I got there. I don't want to use the term 
incorrectly in my application. That's why I'm posting it here.

Best Regards,

Viruthagiri Thirumavalavan
Dombox, Inc.

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