[nSLUG] Three identical multipart borders in one email?

Mike Spencer mspencer at tallships.ca
Fri Nov 2 19:49:18 ADT 2012

Daniel AJ Sokolov <daniel at falco.ca> wrote:

> Today I have received an email that my Thunderbird 16 can not
> display.  It seems to be empty zen-mail, but in fact contains three
> base64 encoded chunks.
> One is text/plain, the second one is text/html and the third one is
> text/calendar.
> All three multipart boundaries have the same string. Does that
> conform to RFC?

Yes. See RFC 1521, p. 34 for an example of multipart/alternative using
a single boundary string throughout. 

> Other multipart emails in my inbox have on[e] boundary string for the
> first part, and one different boundary string for all further parts.

A part of a multipart MIME message *may* have its own Content-Type:
header that includes a second boundary string separating or bounding
sub-parts within that part. 

See RFC 1521, Appendix C, p. 65,  for an example.

I see that I have a correspondent using QUALCOMM Windows Eudora
Version who sends multipart/alternative messages (HTML and
ASCII versions of the same text) structured that way.  But it's an
unnecessary frippery in a case of such a simple message.

(The closing boundary string differs in having two '-' hyphen chars
appended for both primary and secondary (or sub-) boundary strings.)

Not an expert here but I groveled through this stuff once in an effort
to detect deep packet inspection (reported here on NSLUG 16 Feb 2011).

- Mike

Michael Spencer                  Nova Scotia, Canada       .~. 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^

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