[TYPO3-dev] t3lib_htmlmail breaks plaintext version when inline images are attached

[Simon Tuck]

Looking for some love here...

I've done some research on the subject and tested the format 
t3lib_htmlmail sends on a few other mail clients. I believe that the 
definition of the mail structure for "Plain + HTML + image" is wrong in 
t3lib_htmlmail. According to t3lib_htmlmail the correct strcture for 
"Plain + HTML + image" is:

  * 	multipart/related (m/a, cids)
  * 		multipart/alternative (text, html)


Imo it should be:

multipart/alternative
           text/plain
           multipart/related
                   text/html
                   embedded object one
                   embedded object two
                   ...

RFC 2257 (http://www.rfc-editor.org/rfc/rfc2557.txt) states:

[...] When the start
    body part of a multipart/related structure is a multipart/alternative
    structure, and that structure contains at least one alternative body
    part which is a suitable atomic object, such as a text/html resource,
    then that body part SHOULD be employed as the root resource of the
    aggregate document. [...]

In other words the html body part of the multipart/alternative should be
employed as the root resource for the multipart/related and not the
entire multipart/alternative.

See also
http://search.cpan.org/~bbc/Email-MIME-CreateHTML-1.026/lib/Email/MIME/CreateHTML.pm 

  for an example of a rfc2557 compliant mail construction